DERMATEMYDID^i. 247 



left hyoplastron, a large part of" the right hypoplastron, and the hinder ends of both xiphi- 

 plastra. Of these, there is now in the collection at Rutgers College only the hyoplastron. 



The species is characterized by the thinness of the bones, being approacht in this respect 

 only by A. agilis. The hyoplastron has a thickness varying from 10 mm. to 12 mm. Accord- 

 ing to Leidy the hypoplastron varies in thickness from id to 14.5 mm. 



From the portion of the hyoplastron present it appears that the width of the anterior lobe 

 at the base was about 180 mm. The hyoplastral bones joined along the midline a distance of 

 about no mm. The entoplastron had an approximate width of 65 mm. and extended back- 

 ward behind the hyoepiplastral sutures about 40 mm. A sulcus, the humero-pectoral, crosses 

 the plastron 7 mm. behind the entoplastron and is directed slightly backward on its way out- 

 ward. The free border of the lobe is subacute. All the sutures of the hyoplastron appear to 

 have been close and smooth when viewed from below; but, seen from above, they were coarse 

 and jagged. 



The hypoplastra are stated by Leidy to have extended along the midline 5 inches; accord- 

 ing to his figure, 130 mm. The hinder end of the plastron appears to have been narrowed, as 

 in A. beatus. 



This species seems to have most resembled A. agilis; but the entoplastron of the latter is 

 considerably broader, less abruptly rounded, and the notch was more open. In A. syntheticus 

 and A . punctatus the humero-pectoral sulcus crosses on the entoplastron. 



This species differs from Cope's specimen of//, beatus, from Medford, in having a narrower 

 entoplastron. In the latter the width of this bone was about equal to the length of the suture 

 between the right and left hyoplastra. In A. pravus the width was equal to only two-thirds 

 the suture between the hyoplastra. In other respects the two species, so far as known, appear 

 to agree. Altho Leidy has restored in outline the anterior lobe of A. pravus as being very 

 narrow, it may in reality have been much broader. 



Adocus? lineolatus Cope. 

 Figs. 308, 309. 



Adocus? lineolatus, COPE, Bull. U. S. Geol. and Geog. Surv. Terrs., I, No. 2, 1874, p. 30; Ann. Report 



U. S. Geol. and Geog. Surv. Terrs., 1873 (1874), p. 454; Vert. Cret. Form. West, 1875, p. 



92. LAMBE, Contrib. Canad. Palaeont., in (410), 1902, p. 38. 

 Adocus lineolatus, COPE, Vert. Cret. Form. West, 1875, p. 263, plate vi, figs, u, 12. HATCHER, Bull. 



U. S. Geol. Surv. No. 257, 1905, p. 75. 

 Compsemys lineolatus, COPE, Bull. U. S. Geol. and Geog. Surv. Terrs., Ill, 1877, p. 573. HAY, Bibliog. 



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



Of the present species very little is known. The name is based on 2 fragments which were 

 collected by Professor Cope, in northeastern Colorado. From Whitman Cross (Monogr. U. S. 

 Geol. Surv., xxvn, 1896, p. 244) we learn that Cope communicated the fact that these and 

 some other fossils had been collected at some point not designated on Bijou Creek. 



Cross is of the opinion that these fossils came from what are called by him the Arapahoe 

 beds, a formation overlying the Laramie. Cope's type of his Adocus? lineolatus is now in the 

 American Museum of Natural History and has the number 1844. Cope's figures represent 

 well the specimens; but since they have been figured the surface has been scraped from the 

 neural, so that its sculpture no longer appears. That of the fragment of plastron remains. It 

 is obscure, but consists of elongated, very shallow pits, four or five in a line 5 mm. long, and 

 arranged more or less in rows and separated by low narrow ridges. The neural has a maxi- 

 mum width of 28 mm. and a thickness of 7 mm. The plastral bone is 8 mm. thick at the 

 sutural border. This suture is coarse and, as Cope says, has a median serrate keel, with pits on 

 each side of it for the reception of processes from the bone with which it articulated. 



Cope stated that the species comes also from the mouth of the Big Horn River, but the 

 present writer does not know of any specimens on which this identification was based. Cope 

 likewise includes the species in his list of Judith River species. Lambe, as cited, reports it 

 from the Belly River beds on Red Deer River, Alberta, British America. His specimens too 

 were fragmentary. Specimens with a sculpture very similar have been brought to the American 

 Museum of Natural History from the Laramie beds of Montana. These were collected by 



