Cope. J 228 [Dec . 21, 



PSEUDEMYS BISORNATUS Sp. 110V. 



This fresh water tortoise is represented by portions of three individuals. 

 These exhibit a rather flattened convex carapace, with marginal bones 

 united (behind the bridge at least), without gomphosis, by fine suture. 

 There are no median or lateral keels. The vertebral bones are nearly as 

 wide as long, and thick ; the costals are thickest proximally and thinnest 

 medially. The marginals are quite stout. The dermal scutal sutures are 

 deeply impressed, especially those defining the marginal scuta. 



The sculpture of the superior surface of the carapace is strongly marked 

 and peculiar. The vertebral scutal areae are smooth, or display only a few 

 obscure ridges directed backwards and inwards, on the proximal portions 

 of the costal bones ; the vertebral bones being smooth. The costal scuta 

 present two forms of sculpture ; posterior to the intercostal bony suture each 

 is reticulated with inosculating sharp ridges whose general direction is 

 longitudinal proximally and transverse distally. The sculpture is Trionyx- 

 like, and rather coarse. The surface anterior to the osseous suture, is orna- 

 mented with raised, parallel ridges, which are separated more widely than 

 those of the posterior half of the scutum, and which do not inosculate . They 

 continue uninterruptedly to the succeeding osseous suture, to be followed 

 again by the reticulate pattern. Thus each costal bone is divided into three 

 areas ; a proximal smooth one, and an anterior reticulate, and posterior 

 ridges arete, separated by a deep sutural groove . 



A posterolateral marginal bone unites subequally with two costals. Its 

 superior surface rises in abrupt convexity beyond the costo -marginal der- 

 mal suture, and from the transverse intermarginal dermal suture. It is 

 then concave to the recurved margin. Its sculpture consists of transverse 

 ridges, separated by grooves of equal width. 



Measurements. M, 



Length of a vertebral bone 035 



Anterior width ot same » . 032 



Thickness of same anteriorly 009 



( antero-posterior. 035 



Extent of median costal j trangverge m 



Median thickness of do 006 



Distal •'• " 007 



Length of a posterior marginal , 030 



Width " " . ... .042 



Thickness " " 017 



This tortoise is at first sight apparently singular in its marks of ornamen- 

 tation. On comparison with existing species, however, it is seen to present 

 an exaggerated condition of the sculpture characteristic of some of the exist- 

 ing Pseudemydes of our Southern rivers ; e. g. the P. elegans. It is more 

 robust in all its proportions than any of these. 



The fossil remains were discovered by my friend, G. W. Marnock, in the 

 pliocene of South-western Texas. 



