Cope.] ""*" [Dec. 2, 



is an obtuse ridge corresponding to the pubis, and a knob answering to 

 the extremity of the ischium, both more prominent than is usual in 

 genera of Emydidse. 



This exceptional combination of characters points to the propriety of 

 separating Adocus as the type of a family equally distinct from the 

 Emydidse and the Hydraspididae, to be called the Adocidse. 



Further characters of the genus have been already pointed out in the 

 later essays above quoted. They are : the free lobes of the plastron 

 narrowed and shortened, furnishing extensive posterior and anterior 

 entrances to the carapace. A series of intermarginal scuta on the bridge. 

 Costal capitula reduced or wanting. 



No recent or even tertiary form of the Testudinata has yet been dis- 

 covered, which possesses the remarkable combination found in this genus, 

 and I think it must be regarded as a generalized group, and as such of 

 much interest to the student of palaeontology. 



The determination of the presence of the intergular plate in this genus 

 enables me to isolate from it the Baptemys of Leidy, whicii is otherwise 

 very similar. This being the case, there is reason to believe that the 

 latter is a Tertiary genus, and not Cretaceous one, as I had before been 

 inclined to suspect. 



The species then are : 



I. With mesosternum deeply received. 



Plastron very thick. A. pectokalis. 



Plastron thin. A. pkavus. 



II. With transverse mesosternum. 



a. Posterior lobe of plastron contracted, long as wide. 

 Plastron of medium thickness. a. beattjs. 



aa . Posterior lobe broader than long, rounded. 

 Plastron thick, sparsely punctate. A. syntheticus. 



Plastron thin, closely punctate. A. agilis. 



Adocus syntheticus. Cope. 



Spec. nov. 



Established on a plastron which lacks the mesosternal, one episternal, 

 and one hyposternal ; also on a marginal bone from the bridge, two im- 

 perfect costal bones, proximally complete, and some smaller fragments. 



The bones of the plastron present that oblique junction of element 

 with element diagonally across the point of crossing of longitudinal and 

 transverse sutures, as has been observed in all the species of the genus, 

 except A. pectoralis. Thus the right hyposternal, besides the usual union 

 with the left, presents a considerable suture for the left hyposternal, and 

 a lesser one for the left xiphisternal. The median dermal suture does not 

 coincide with the osseous behind the hyosternal bone ; but it is consider- 

 ably to the left of it, dividing the xiphisternal bones unequally. The 

 osseous suture is irregular and undulating. The hypo-xiphisternal suture 

 extends abruptly backwards near the margin of the plastron. This 

 margin behind the groin is thinned rather abruptly, with a marginal 



