1870.] '-•^ -* [Cope. 



ON ADOCUS, A GENUS OF CRETACEOUS EMYDID^. 

 By E. D. Cope. 

 ADOCUS, Cope. 



Proceed. Acad. Natl. Sciences, Phila., 1868, 235. 



Character. Anterior and posterior lobes of the plastron abbreviated, 

 narrowed, and not emarginate. Eight paired sternal bones ; twelve ster- 

 nal scuta, the humerals extending anteriorly, the pectorals and gulars both 

 small. A series of plates — " intermaginals" within the marginals, on the 

 sternal bridge. Rib heads, i. e. the capitula, wanting in the species whose 

 costals have been examined. 



This genus was originally described with Emys heatus Leidy from the 

 Cretaceous Green Sand of New Jersey as the type, and its primary char- 

 acter was regarded as the absence of the costal capitula. In the synopsis 

 of extinct reptilia of New Jersey, published in Prof. Cook's Geological 

 Survey of that State, five species were numerated, as follows ; A. petrosibs, 

 Cope, A. flrniiis, Leidy, A. heatus, Leidy, A. pravus, Leidy and J,, agi- 

 lis, Cope. The two species first enumerated having subsequently been 

 found to possess well developed costal capitula, I referred them to Emys, 

 in the "Synopsis of extinct Batrachia and Reptilia of North America," p. 

 126. My specimens of A. agilis being at the time very imperfect, it was 

 not described. 



In the present essay I propose to point out its characters, as well as 

 those of the other sjsecies of the genus. Two species are added, the 

 whole number being then five. One of these is from the Cretaceous de- 

 posits of Wyoming, the others from New Jersey. 



The plastron in this genus presents marked peculiarity. The great re- 

 dviction of the anterior and posterior lobes gives it a form pointing to 

 that of Staurotypus. The anal scuta are of large size, and the humero- 

 abdominal scutal suture (in A. agilis) extends across just in advance of the 

 inguinal notch. The abdominal is the widest pair of scuta, in conse- 

 quence of the relatively great longitudinal extent of the bridge ; tlieir an- 

 terior outline falls a little behind the axillary notch. The humeral sciita 

 have a remarkable anterior extent, so much so as to lead to the suspicion 

 that they were confluent with the pectorals, or perhaps wanting. In the 

 case of A. pecioralis, having only the hyosternal bones, I was induced to 

 think that they were really the pectorals, and that the abdominals were 

 the true humerals, as is seen in the genus Pleurosternum ; the posterior 

 position of the humerals in the latter being owing to the existence of an 

 adchtional pair of sternal bones. An examination of that structure in A. 

 agilis and A. wyomingensis, dispels this view, and shows that the true pec- 

 torals are much shortened, and have an anterior position, and that the 

 gulars are also small- and narrowed, the genus approaching Chelydra in 

 these respects. 



The lateral series of abdominal marginals is seen in the existing genera 

 Macrochelys and Deimatemys. The affinity of Adocus is to the latter, 

 but the entire acuminate free lobes of the plastron, distinguish it well. 

 The lateral marginal scuta in A. agiis, A. leyomingensis and A. pectoralis 



