186 Mr. M. A. C. Hinton on

Allied to P. stalalTmolgtera , St~l, but with the opereula larger, distinctly narrowed, and obtusely angular ly pro- duced at their apices, and there broadly black; pronotum much narrower between the apices of the lateral angulate margins.

81tnon!lm{cal _Note. DalMra crassa, Dist. Ann. & Mag. Nat. Hist. (7) ii. p. 303 (1898).

Schouteden (P~ev. Zool. Aft . ii. p. 107 (1912), in enumerat ing this species from the Transvaal , writes " cette esp~ee a ~t6 d6erite eomme Meton~mia (Dalsira ol.) par I ) i s tant ."

I described it as .DaIMra (supra) in 1898, and, as the genus Metonymia was only proposed by Ki rka ldy in 1909, I cannot well be charged with an impossibility.

X V I . - - O n some I~eraains of Rodents from th, Red Crag of Jb'uffolk and front the ~/orfolk ~h'orest-.Bed. B y MARTIN A. (3. HI2~TON.

[Plate VIII.]

:IN the present paper some imp.ortant fossils from the l~ed- Crag and the Forest -Bed series of ~or fb lk are described. These materials appertain to the genera Castor, •rogon- therium, and Sciurus. I have to return my best thanks to ]Rajor Moore, of Fclixstowe, Mr. A. C. Savin, of Cromer, and Mr. Gilbert Whi te for the loan or gift of the specimens described.

1. CASTOR.

(a) Castw; ~eter£or, Lankester .

,4_ f ragmenlary right ramus in tile collection of Major Moore, from the Red Crag of Wocdbridg% Suffolk, is referred to this species. In this specimen (P1 .VI I I . fig. ! ) g-i, ~--:-i. l, and part of

are in place. The crown of r.--:2 is fully developed, while m.---t has well-devel~ped fangs(fig. 1, " a " ) . Each tooth has one outer and three inner folds and, as in C.j-~ber, the enamel is uncrimped. Tile outer fold is persistent, as usual in Castor ; tim anterior and middleinner folds of ~ are also long persistent as in C. fiber. The posterior inner fold of ~ and all three

n,~To~. A~n. ~" Ma~. ~Yat. [li,~t. S, #. Vol. X l l l . Pl. VIII .

p . 4 m . I m.~. "

"0 A

Fig. 1. B

b b Fig. 2. Fig. 3.

~ ~ Fig. 4.

O Fig. 6.

=. c .fir

8.

B A •

Fig. 7.

a. a . t . 5 2

D

A B 6

Fig. 8. Fig. 10. ~f . A. C. H i n t o n de l .

Fig. 6 (b).

Fig. 6 (a).

a

5 2 4

G

Fig. 9.

some Remains of Rodents. 187

inner folds of m--:-i die out on the sides of the teeth a little below the present grinding-surface, so that , with a little fur ther wear,

lhe~lfa~liod: ~ :u lmdb: c]~tt~:r~:dg~t°:tn:m~los'::rS~:rtlSy"t h~, : ~n s

G.fiber; its anterior surface is l ightly furrowed by a weak vertical su lcus- - the last trace of a former more complex condition of the anterior loop.

Dimensions : - -

C. veterior. C. flber. 111111, ]~Efl.

Antoro-posterior length of v~ . . . . . . . . . . . . 10 9"5 Width of ~.4 behind . . . . . . . . . . . . . . . . . . . . 8 8 Antero-posterior length of ~ . . . . . . . . . . 7 8'5

' n In the two upper premolars, from the Red Crag of 8utto , upon which s i r E. R a y Lankester based his C. veterior ~, :Mr. E. T. Newton found that " t w o of the three outer folds of enamel are only" open to the exterior for a short distance from the summit of the t o o t h " ' l ' ; the lower teeth now described present corresponding characters, and may there- fore be referred to C. veterior. The difEerencesin the number of folds reduced peripherally in the individual teeth, viz., all three inner in ~75. t, two outer in p-Ti, and one inner in p~, are in harmony with our experience of such reductions in other rodents.

I n the relatively large size of p-Ti, and in the early conversion into " i s l e t s " of the inner folds of lower and the outer tblds of upper cheek-teeth, C. veterior makes some approach den: tally towards Trogontherium; in the latter all the enamel folds are so reduced during wear, and in its later species there is a great increase in the size of tim animal.

C. isslodorensis, Croizet, is stated by Pomel :~, Gervals §, and Bosco II to be hardly or not at all different from C.fiber, so far as it is known. C. prcefiber, Deperet;¶, from the ~Pliocene of Rousillon, is distinguished by its slender molars and the absence of a third troehanter to the femur. To one of these two forms the Red Crag beaver with persistent enamel-folds, provisionally referred by Newton to C. flber~ not improbably belongs.

~ Lankester, Ann. & Meg. Nat. t]ist.(3) xiv. p. 365 (1864). :Newton t ' Vertebrata of the :Pliocene Deposits of Britain/ p. 50

Os9~). Pomel, ' Catalogue M~thodique/p. 20. (~ervais~ Zool. et Pal. Fran~. 1859, p. 20.

~ Bosco, ~ Palmontographi~ It~lica,' v. p. 89. ¶ Deperet~ M~m. Soe. G~ol. de France, Pal~ontol. no. 8 (1890).

188 Mr. M. A. C. tIinton on

(b) ForestoBed Beavers.

Forsyth Major* has shown that two species of Castor occur in the Forest-Bed horizon exposed at East Runtonj Norfolk. One, characterized by its broader incisors, sIightly larger cheek-teeth, and, above all~ by the " complex and elegant pl icat ion" of the enamel of its molars, is identical with C. pllcldens, Major, a species described from the Upper :Pliocene of the Val d'Arno ; the other, with narrower incisors, smaller molars, and much less plicated enamelj makes a nearer approach to the recent species, and it is the only form which has been found hitherto in the Upper Freshwater Bed at West Runton. Recently Mr. Savin has found in the latter deposit two young upper cheek-teeth of Castor)each being either the right ~" 1 or ~' 2 (P1. VI I I . figs. 2 & 3). Each tooth presents the usual enamel pattern, and in each the enamel, as exposed at the grinding-surface (figs. 2 a, 3 a), is free from plication. An examination of their bases shows that, while in tile smaller tooth ttle enamel would remain unerimped (fig. 3 b), in the larger one (fig. 2 b) it acquires in deeper strata of tile crown the complex and elegant plication of C. plicidens. Bosco~ has shown that the jaw from the Val d'Arno, on which Fors:yth Major based his 0. rosime$, is, in fact, a young jaw of C. plleidens; the enamel at the grinding- surface of the little-worn teeth of this jaw is free from plica- lion, but a section made through the basal parts of the teeth shows that the typical plication is developed in the deeper portions of the teeth, just as in the West Runton specimen. I t may be mentioned, further~ that whereas in the molars of the lower jaw from East Runton figured by Forsyth Major tho plication principally affects the enamel of the first and third inner folds, in ttle West Runton tooth all three of the corresponding outer f61ds display it.

]~ir. Savin possesses a large right ramus from the Forest Bed of Bacton with all the teeth in place. It belonged to an old individual. The molars are greatly worn and some of them are mutilated ; their crowns still show, particularly in the antero-internal fold of each tooth, traces of a strong plication of the enamel. The incisor is very broad. This jaw also may, perhaps, be referable to C. plicidens.

¢* :Forsyth l~Iajor, Proc. Zool. Soc. 1908, p. 630. ~ Bosco, op. tit. p. 88. ÷ Forsyth Major, Arch. per l'antrop, e l'etnografia, -col. vL 1). 345 (187~).

some Remains of Rodents. 189

Dimensions : ~ m m ,

Alveolar length of cheek-teeth . . . . . . . . . . . . . . . . 89 Breadth of incisor . . . . . . . . . . . . . . . . . . . . . . . . . . 9"3

~at erowa ~.. 11×8"5 iastema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

0. plieidens appears to be a specialized offshoot which arose and became extinct in the Upper Plioeene period. Forsyth Major tells us that in aged teeth of C.fiber a mode- rate plieation of the enamel makes its appearance. G. plici- dens seems thus to have rapidly acquired a dental feature which tile recent beaver, had it been left alon% might have developed in the fullness of time.

2. Trogontherlum cuvlerL Among tlle specimens fi'om the Upper Fresh~¢ater Bed of

Wes tRunton in Mr. Savin's private collection are three fi'ag- mentary and very young incisors which, despite their small size, apparently belong to the Tro~lontherium. Two of them (PI. VIII . figs. 4: & 5) are sharply curved and are evidently left upper incisors. Their sectional diameters increase rapidly posteriorly, and they are characterized by their convex faces of rugose enamel. The outer surfae~ in each is traversed by a narrow groove along the junction of the enamel with the dentine, and there are fainter indications of a similar feature on tile inner surface. The tip of the smaller and younger specimen presents a round, rather uneven, wearing surface. The larger specimen has been in use long enough to have lost by wear that portion of the erown which is represented by the smaller tooth, and, although the end is now somewhat mutilated, to have acquired a normal disc of wear.

The third specimen is very small, its brgken base not being wider than the tip of the smaller upper.incisor just described. :It is straighter than either of tile others, and may be deter- mined as the left lower incisor (P1. VII I . fig. 6). The enamel of lhe convex anterior face is finely rugose ; there is a narrow groove on the outer and a still narrower and less distinct one on the inner surface. The tip (fig. 6 a & b) is quite unworn and consists of two little tubercles~a higher inner and a lower outer one--separated from eaeh other by an anterior and by a p~sterior valley. These valleys extend downwards upon the front attd hinder surfaces of the tooth for a distance of about 1 mm., and then die out. The posterior valley (fig. 6 a) is a deeply re-entrant V-shaped notch, cutting the

190 Mr. M. A. C. Hinton on

crown to ifs centre ; the less deeply re-entrant anterior valley (fig. 6b) has its floor raised as a little rib. Each valley contains a little eement. The hinder sides of the tubercles and the posterior valley are invested with a thin coat of enamel, hut whetlmr the latter extends over the apices of the tubercles or not is uncertain. The groove.~ of the outer and inner surfaces--persistent features in adult incisors of Trogon- therium--are seen to. start from the summit.

In dlseussing the grooved upper incisors of Lagomorpha Forsy th Major o has stated that : I , , The incisors provided with enamel-folds point back ~owards euspidate incisors, for tile enamel-folds of lophodont and laminated teeth are obviously tile derivatives and homologues of the ' va l leys ' separating the cusps or tubercles." In this connection it is of very great interest to find traces of the primitive complexity in the unworn incisor of Trogontherium. I t may be that in some eases, where one or more grooves channel the anterior faces of the incisors, their persistence is due to the fact that such grooves are of use to the animal retaining ~hem, as Tullberg ~" suggests ; but, in my view, it is wrong, to regard such a g.roovc, as a new feature produced in any gtven ease, because it is there useful. I t is a fact that frequently in Lagomorpha and in other rodent~ more or less distinct traces of a posterior incisor valley can be fonnd iu the form of a shallow sulcus, which, devoid of enamel, can hardly be of any functional importance. Further , in many voles vestiges of vanished valleys can be found as narrow, shallow, well- defined, and persistent grooves upon the sides of their molars ; in these eases it is only by a s tudy of unworn or little-worn teeth that the true signi6canee of such, at first sight, trivial features becomes apparenL

One of the most interesting of Mr. Savin's recent acquisi- tions from the West-Runton deposit is a foot-bone, which I have determined as the r ight navieular of Trogontherium--a part hitherto unknown. In 1)1. V I I I . fig. 7 four views of the fossil are given, with corresponding views (fig. 8) of the navicular of Castor j~ber. Generally the fossil closely agrees with the recent bone in form and in the number and arrangement of the faeettes ; it differs principally in having the articular surfaces much larger, the posterior spur, on the other hand, much smal lo r~so that, as a result, its absolued size is but little greater. Anteriorly it is wider, posteriorly

Forsyth Major, Trans. Linn. See., Zool. ser. 2, vol. vii. p. 470 (1899). T Tullberg, ' Ueber das System der Nagethiere,' p. 363.

some Remains of Rodents. 191

narrower, so that its plan is triangular instead of nearly rectangular. In the beaver the astragalean faeette is a circular, rather deep basin, with a well-defined posterior rim, 9eeupying about half of the proximal surface ; in the fossil it is a rather shallow, irregularly shaped concavity, with an ill-defined posterior margin occupying fully two-thirds of tile proximal surface. Tile distal surface presents th~ usual three facettes for the cunei[orms, and these have a greater antero-posterior extent than in fhe beaver. The facette for cuneiform I I I . is nearly plane instead of" concave antero- posteriorly; that for cuneiform II. is relatively wider and gently convex from behind forwards~ instead of nearly flat. Tile faeette for cuneiform I. is large, crescentic, and concave, forming the antelior side and roof of a profound notch which cuts almost through the bone from the distal to tile proximal surface; in the beaver this notch is much less deep and the facette is greatly reduced and convex, only the anterior part of the facette of the fossil being represented. On the other hand, in the beaver the anterior lace of the greatly developed descending process or " spur " boars a small addi- tional faeette for the posterior margin of cuneiform I., which is not represented in tile fossil. Between the superior border of the chief faeette for cuneiform I. and the astragaleart surface there is in the beaver a rather large, slightly inclined, oval facette for the "naviculare tibiale"; in the fossil this faeette is also present, but is narrower, triangular in shatJe , and highly inclined. The outer (fibular) side of the bone is occupied anteriorly by the euboid faeette. In the beaver this is relatively short, low behind, its plane nearly vertical, and very slightly concave antero-posteriorly. In the fossil it is longer, much higher behind, its nearly vertical anterior portion faces backwards and outwards, and its oblique hinder pat't faces slightly forwards, downwards, and outwards ; the outer border of the bone, when viewed from below, conse- quently appears widely notched instead of straight or gently concave. Tile posterior spur is much less developed than in the beaver; i.~ the latter its plan is nearly square, its flat upper surface ascends posteriorly, while below it is produced as a massive projection descending considerably below the general level of the distal surface ; in tile fossil it is narrower, its upper aurface is rounded and shelves away behind and laterally, while below the descending process is little developed and scarcely attains the level of the distal surface. The measurements recorded in the following table bring out many important distinctions : ~

192 M,'. M. A. C. H i n t o n on

Measurements of navicular (millimetres).

Antero-postorior diameter . . . . . . Transverse width in front . . . . . .

behind . . . , . . . . Widt' " of astragalean facette . . . .

,, facette for eun. III. I I . . . . .

Antero-posterior diameter of fa- cette for curt. I I I . . . . . . . . . . . . .

An~ero-posterior length of euboid face tte . . . . . . . . . . . . . . . . . . . .

HeL~ht of euboid facette at post.- ex"ternal corner of facette for cun. I I I . . . . . . . . . . . . . . . . . . . I

Height of cuboid facette behind .1 Least distance between facette for I

eun. I IL and front edge of I proximal surface . . . . . . . . . . . . /

Height of spur behind . . . . . . . . . . | !

Trogontherium. Forest Bed: W. Runton.

Absolute.

19"7 15"7 7"1

11"7 8"6 6"6

6"8

12"0

5'0 6'6

Reductions.

100 68 79'8 34 36"1 60"8 59'4 100 43"7 73"5 33"5 56"4

34'6 58"2

61 0'2

25 "4 49 '8 33"5 56"4

4 3 6 6"2 '4

Castor. Alluvium : Tlmmes.

5"1 7"3

Absolute. Redtl

18"7 100 13"7 73"4 8'6 46 8"6 46 9'0 48"2 5 0 26"8

5"7 30'5

10"5 56"2

5'2 27'8 4"8 25"7

4"0 21 "4 11"0 58"8

ctions.

217 159 100

100 105 582

66"2

1"22

60"5 55"9

46"5 128

F r o m this descr ipt ion it is clear tha~ the fossil nav ieu la r be longed to an animal possess ing close affinities wi th the b :aver ; never theless , the differences observed are of gener ic impor tance . A compar ison of tile a r t icu la t ions shows tha t the fossil tbrmed pa r t of a considerably l a rge r foot than that or' Castor. Tile on ly la rger beaver - l ike rodent known from the F o r e s t Bed is the Trogontherium, and, in v iew of a l l the facts, no reasonable doubt can remain that the fossil is r i gh t l y refer red to this genus . I n t i le beaver t i le fourth me ta t a r sa l is ttle longes t and stoutest~ t i le th i rd is l i ~ l e shorter though more s lender , the second and fifth are much smaller , and t e a t of the ha l lux is s t i l l fur ther reduced. F r o m the fact tha t tile faeet te for cune i form I I I . is narrower , while thoso for e u , e i f o r m s I I . and I . are wider and mo,'e ex tens ive ly developed in t i le fossil, we may infer tha t the d i spar i ty in tile size of tile th ree cuneiforms, and consequent ly of t i le first, second, aml th i rd me ta t a r sa l s which they suppor t , was less m a r k e d iu tlle Trogontherium than in tile beaver. The s l igh te r deve lopmen t of the poster ior spur in the fossil be tokens less power fu l ly deve loped flexor muscles. Ti le en la rgeu lea t of

some Remains of Rodents. 193

the third and fourth toes in the foot of the beaver is a feature seen also in the feet of many other aquatic mammals, and is a specialization for swimming. From the circumstance that, judging from the navieular, these two digits were less specially favoured in Trogontherium, we may infer that the latter was less aquatic than Castor.

Since writing the above paragraph I have read Owen's account* of some limb-bones referred by him to Trogontherium. They included the humerus, femur, tibia and anchylosed fibula, and the calcaneum. The humerus was much larger proportionally, tim femur much shorter in relation to the tibia, than in Castor. The femur is clearly much less specialized, differing principally in the smaller and more highly placed third trochanter, the rounder and thicker lateral bo'rders of its distal half, and its slighter distal expansion. The tibia is longer and has a shallower posterior groove, and the fibula is more extensively anchylose~ with it below. The calcaneum presents features analogous to those described in the navicular. As in the latter the posterior non-articular part; is shorter relatively, the articular part more largel) developed; it is also broader, and there are similar differences in the form and curvature of the facettes. I t is with satisfaction that I note that Owen inferred " from the femoral modifications that the Trogontherlurn was less aquatic and a swifter mover upon land than the beaver."

Sciurus whitel, sp. n.

~ a n y years ago Oswald Heer t noticed that some of the fir-cones from the Forest Bed bore marks which appeared to indicate that they had been gnawed by squirrels. Tile only additional, and quite doubtful, evidence of such an animal in the Cromerian fauna which Mr. Newton was able to record in 1882 was that of a humerus in the Green Collection from Ostend, Norfolk ; this bone agrees closely in form with that of ~. vulgaris, and it is not certain whether it came from the Forest Bed or fi'om a recent alluvial deposit. Until the discovery to be described here was made, no further trace of a squirrel has been met with in the Forest Bed. A fqw years ag% when he was collecting from the thin bed known as the

~ Owen, Geol. Mag. dec. 1, vol. vi. p. 52 (1869). Newton, " Vertebrata of the Forest ]3od,',' ])lena, Geol, Survey, 1882,

p. 92. Ann. & Mag. _N. Hist. Ser. 8. Vol. xiii. 13

194 Mr. M. A. C. Hinton on

" Monkey Grave l "* - - t l l e uppermost part of the Upper Freshwater-Bed at West Runton, Norfolk,--Mr. G. White was fortunate enough to find a minute tooth; its small size, yellowish colour, and form, resembling as it does a few agglutinated particles of tile sand in which it was embedded, says much for the sharp sight of my friend. Mr. White very generously presented tile specimen to me. It turns out to be the right ~ of a squirrel. It differs importantly from the ~ of S. vulgaris, and indicates a species which, when more fully known, will probably not be able to find a place within tile genus Seiurus as restricted by modern mammalo- gists. For this Forest-Bed species I have pleasure in pro- posing the name of S. whltei.

In ~q. vulffaris (P1. VIII . fig. 9) the outer border of p. 4 is formed by the four cusps called by Winge 1, 4, 2, and 5 ; of these 4 and 5 are the largest and most lofty, 1 is nearly as stout though lower than either, while 2 is minute and on its way to disappear. The inner side of ~ is formed by a single very large and lofty cusp (Winge's 6), which Forsyt5 Major t has shown to be a compound of at least three inner tubercles which have fused together. Between the outer cusps and the inner cone is a series of transverse ridges (formed out of a modified median series of tubercles, and compl4sing, inter alla, the "proto-" and "meta-eonules") , viz., a low one forming the anterior border of the tooth from cusp 1, two higher ones from cusp ~, and the anterior edge of cusp 5 respectively, and a low one forming the posterior border from the hinder edge of 5 ; between these ridges are three trans- verse valleys, of which the central one, for the reception of the chief cusp of the opposed tooth, is the widest and deepest.

In the fossil (PI. VIII . fig. 10) the same elements are present, but the transverse arrangement is less perfect. Cusp 1 is much smaller, as in some species of Tamlas ; it is compressed from before backwards, and prolonged inwards as a rounded ridge whicti dies out with the first transverse valley at a point less than halfway across the crown. The remainder of the front border of the tooth is formed by the " proto-conule/~ which here retains more of its tubercular character and indepen.: dence, being more forwardly placed and separated from cusp 4 by a conspicuous cleft. Gasp 2, though very low, is stouter. The meta-conule is stouter and more indepen- dent ; externally it is placed further back, the hinder trans-

Hinton, Geol. Mug. (lee. 5, vol. v. p. 440. Forsyth Major, Prec. Zool. Soc. 1893, p. 182,

some Remains of Rodents. 195

verse crest s ta r t ing f rom its posterior pa r t instead of f rom cusp 5. As a resul t of these difEerences the anter ior and posterior t ransverse val leys are less extensive, the central one, on the other hand, wider and deeper than in S. vu lqar is . Viewed from the f ront , the fossil is seen to be ra ther more b rachyodon t than the recent tooth. L i k e the lat ter , the fossil has three roots, viz., a large f a n g suppor t ing the inner cone and two small ones on the outer s ide ; in the tbssil the outer fangs are of app rox i m a t e l y equal size, but in ~S'. vul.qaris, owing to the greater size of cusp 1, the antero-externai fang is stouter than the postero-external one. As the following dimensions show, the fossil is considerably smal ler than the recent tooth : ~

Antero-posterior length, outer border . .

Transverse width (6-4)

S. wMtei.

m m °

1'98

2"2

~. vu~Tarls.

] T i m .

2"25

2"42

EXPLANATION OF PLATE VIII .

~g. 1. Castor veterior, Lankester. Part of a right ramus, with p. 4, ra. 1, and ~-.~, from the Red Crag of Woodbridge, Suffolk. Major Moore's collection. A, inner, 13, outer view ; C, crown view of cheek-teeth.

-Fig. 2. Castor plicidens, Forsyth Major, from the Upper Freshwater Bed of West Runton, Norfolk. a~ crown, 6, basal view.

Fig. 3. Castor sp., from the Upper Freshwater Bed of West Runton. a, crown, b, basal view.

Figs. 4 & 5. Trogontherium. Lateral and sectional views of two young left upper incisors from the Upper Freshwater Bed of West Runton.

I~'9. 6. Trogontherium. Left 1,wet incisor from the Upper Freshwater Bed of ~Vest Rtmton. 6 a. Posterior view of tip. 6 b. Ante- rior view of tip. (6 a and 6 b much enlarged.)

~ 9 . 7. Trogonthel~um cuvieri, Fischer. Right navicular from the Upper Freshwater Bed, West Runton. A=proximal, B=dist¢l, C----tibial, and D----fibular views. Facettes: a, astragalean; c, euhoid ; I lL, II., and L, cuneiform, n.t., naviculare tibiale.

-Fig. 8. Castor fiber, Linn. Right navicular from the alluvium of the Thames. Lettering as in fig. 7.

.Fig. 9. Sciu,~us vtdgaris ~ Linn. Right pm. 4, recent. × 9. Sis. 10. 8ciurus wMtei, sp. n. Right pro., from the Upper Freshwater

Bed, West Runton. × 9.

(Except where otherwise noted, all figures are of natural size.)