Cope. | 228 [Dee. 21, 
PSEUDEMYS BISORNATUS sp. nov. 
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 areze 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 genera] 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 ares, separated by a deep sutural groove. 
A postero-lateral 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........... 66. c eee eee eee e 035 
Anterior width of Samesci:-.s)eecieeawiee ces cae sages oe 032 
Thickness of same anteriorly .......... 0... eee eee 009 
Bxtent ofmeian costal {rangyerse vss at 
Median thickness of do... 6.6.0.0 fe ee cece cece e eee eee 006 
Distal a OE esata va tn sahbeaye eee elatetbie. negsecbeateiie’a 007 
Length of a posterior marginal..............00- ie aaa -030 
Width ee 0g HK BSERES BES TEE AR eee 042 
Thickness * SEND seleva dda wish ws abvaroeneuseaual th Ba 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. 
