DERMATEMYDID.*. 235 



In 1902, Mr. Barnum Brown, of the American Museum, collected a few fragments of this 

 species in Laramie beds on Hell Creek, Dawson County, Wyoming. One is the first right 

 peripheral (fig. 293). The individual (No. 1085 A. M. N. H.) was a relatively small one. The 

 fore-and-aft extent of the bone is 23 mm., and the thickness of the hinder border, 5 mm. The 

 free edge is acute. The first marginal scute is only 5 mm. antero-posteriorly where it joins the 

 second. The latter widens to 9 mm. at the suture between the first and the second peripherals. 

 On the under side of the bone the sculptured, horn-covered surface is about 7 mm. wide at 

 the suture with the second peripheral, but toward the nuchal it narrows to 3.5 mm. 



Of the bridge peripherals there is a portion of one in the American Museum, No. 998, 

 collected by Mr. Brown in 1900, in Laramie deposits of Wyoming, about 40 miles west of 

 Edgemont, South Dakota. This fragment (fig. 294) shows that there was no sharp carina 

 above the bridge, but an obtuse, rounded ridge. Fig. 2, plate 34, represents what is probably 

 the distal end of the fourth costal. Besides the descending sulcus there are again seen some 

 irregular loops coming up from the contiguous peripherals. 



Of the plastron there are only fragments known. Fig. 295 represents what appears to 

 be the left outer extremity of the hyoplastron of a young individual from Hell Creek, No. 

 1015 A. M. N. H. The zigzag sutural border is for articulation with the peripherals, appar- 

 ently the third, fourth, and fifth. This border is only 2 mm. thick. The longitudinal sulcus 

 is that which passes from the axillary to the inguinal notch. The short branch on the right 

 appears to be the pectoro-abdominal. The three scute areas on the left may be inframarginals 

 or they may be marginals. If inframarginals, they extend wholly beyond the plastral bones. 

 On the inner side of this bone is seen a portion of the strongly developt buttress which rose to 

 the border of a costal, probably the first. It is possible that the bone here described really 

 belongs to the inguinal region. In either case there is indicated the absence of a mesoplastron. 

 On the mesoplastron of Glyptops and of Baena there is one inframarginal. There are three 

 on the bone above described. There would thus be seven probably on each bridge. 



It will be seen from the descriptions given here of this species that it is very imperfectly 

 known. Additional materials ought to be sought by collectors. Evidently it was a species 

 that attained a considerable size and which, when grown, possest a thick shell. Its sculptured 

 upper and lower surfaces must have rendered it a beautiful animal. 



Compsemys? obscura (Leidy). 

 Plate 34, fig. 4. 



Emys obscurus, LEIDY, Proc. Acad. Nat. Sci. Phila. 1856, p. 312; Trans. Amer. Philos. Soc., xi, 1860, 

 p. 153, plate xi, fig. 4. COPE, Bull. U. S. Geol. and Geog. Surv. Terrs., in, 1877, p. 573. 



Compsemys obscurus, COPE, Trans. Amer. Philos. Soc., 1869, XIV, p. 124; Bull. U. S. Geol. and Geog. 

 Surv. Terrs, I, No. 2, 1874, p. 30; Vert. Cret. Form. West, 1875, p. 261. HAY, Bibliog. and Cat. 

 Foss. Vert. N. A., 1902, p. 437. 



This species is retained here under the genus Compsemys because it has already been 

 placed there by Cope and Leidy and because we do not know where else to place it. There is 

 little evidence that it is closely related to Compsemys victa and there is no probability that 

 it is an Emys, in the modern acceptation of that term. 



Leidy's type of his Emys obscurus was found by Dr. F. V. Hayden at Long Lake, in the 

 present state of North Dakota, in deposits that are now regarded as belonging to the Laramie. 

 The writer does not know where the type is to be found. The part figured and described by 

 Leidy is a portion of a costal plate, extending from the costo-vertebral sulcus to the costo- 

 peripheral suture. This costal is 33 mm. wide, 60 mm. long from the sulcus to the distal end, 

 and little more than 3 mm. thick. The surface is described by Leidy as being smooth. His 

 figure shows that the sutural borders were markt by fine striations at right angles to the 

 sutures. 



In the American Museum of Natural History there are the proximal ends of 2 costals 

 which were found by Mr. Barnum Brown, in 1902, in Laramie deposits, on Hell Creek, 

 Dawson County, Montana. These are identified as belonging to the species here described. 

 One of these fragments (plate 34, fig. 4) appears to belong to the second left costal. It is 31 



