THAI.ASSEMYDID^E. 



'55 



(Geol. Surv. Maryland, Eocene, 1901, p. 97. pi. x, fig. 7) has repeated Dr. Clark's words and 

 figured one fragment. The materials are generically indeterminable. 



Lytoloma angusta Cope. 

 Plate 28, figs. 5, 6; text-figs. 191, 192. 



Chelone sopita (in part), LEIDY, Smithson. Contrib. to Knowledge, xiv, 1865, p. 105, plate xix, fig. 5. 

 Lytoloma angusta, COPE, Amer. Naturalist, III, 1869, p. 105 (nom. nud.); Ext. Batrach., Reptilia, Aves 



N. A., 1869, p. 145, plate xi, figs, i, ib; Vert. Cret. Form. West, 1875, p. 257. HAY, Bibliog. and 



Cat. Foss. Vert. N. A., 1902, p. 442. 



Cope's first mention of this species was in the American Naturalist, as quoted above, but 

 this mention was made only incidentally and what was said is not sufficient to distinguish 

 either the species or the genus from various other turtles. When he came to describe and figure 

 the species Cope stated that his materials consisted of three peripheral bones, a fragment of a 

 costal, and a lower jaw. He says that the costals and marginals were found at the same time and 

 place as the jaw and probably belong to it. It seems that he regarded the peripherals as the 

 type of the species, and since he figures only one of these, this especially must be taken as the 

 type. That he so regarded the peripherals is evident from the fact that 

 from peripherals alone of this species and L. jeanesi he drew all his generic 

 characters. Further proof is afforded by the specimen of the jaw itself, 

 which bears, in Cope's writing, the label "?Lytoloma angusta Cope, Bir- 

 mingham, N. J." In case he had lookt upon the jaw as the type he could 

 hardly have questioned its belonging to the species. It is wholly prob- 

 able that at least the figured peripheral and the costal belong with the 

 jaw; and until it has been shown that they do not, all may pass as types. 

 These specimens were obtained in the upper greensand beds of the Creta- 

 ceous, at Birmingham, near Pemberton,New Jersey. Inasmuch as the jaw 

 is labeled by Cope as coming from Birmingham, it is probable that the 

 specimens were obtained from some marl-pit between the two towns. 

 They are now in the American Museum of Natural History and bear the 

 number 1133. 



The figured peripheral (plate 28, fig. 6) is said by Cope to belong to 

 the left side, but on the bone itself he has written "5 R," from which 

 it appears that he regarded it as the fifth of the right side, and such it 

 seems to be. It has a length, along the acute free margin, of 67 mm. A 

 section of the bone is triangular, and therefore it shows three faces (fig. 

 , -j^ e v | scera j f ace j s 22 mm w j ( j e) SOIT1 ewhat concave, and contains 



in the hinder halt " of the bone a dee P C nkal P k f r the rib - end of the 

 tn ' rd costa '- The upper face is slightly concave at right angles with the 

 free border, 22 mm. wide at the anterior end, 29 mm. at the posterior. 



191. Section through fifth The j n f er j or f ace is slightly convex and 32 mm. wide at each end. 



sh e own Ph b C y ra inte P r- Another peripheral (fig. 192) is markt by Cope " ?2 R." It has a 



rupted line. length of 70 mm., a thickness at the visceral face of 16 mm. at one end 



192. Supposed second anc j ^ mm at t h e otner- fhe upper and lower faces are somewhat con- 



vex. In the free border there is a broad emargination. At the bottom 



of this emargination the bone is 28 mm. wide. At one sutural end the width is 34 mm. There 

 is no rib-pit in the visceral face. The peripheral, supposed by Cope to be the fourth, is not 

 now with the other bones. 



The fragment of costal has a width of 47 mm. near the sutural border for the neural. At . 

 the middle of the width the thickness is 10 mm.; at the sutural border it is about 4 mm. As 

 stated by Cope, there is present the sulcus bounding one of the vertebral scutes. From a 

 comparison with the figure publisht by Wieland, and here reproduced (fig. 196), this costal is 

 believed to be the sixth of the right side. The outer angle of the vertebral scute is placed near 

 the hinder sutural border of the bones, at a distance of 50 mm. from the neural. 



The lower jaw (plate 28, fig. 5) is of the greatest interest. It is considerably eroded and 

 does not lend itself well to illustration. It is remarkable for the great length of the symphysis, 



FIGS. 191 AND 192. 



type Y. 



