47'' 



FOSSIL TURTLES OF NORTH AMERICA. 



of the hyoplastron, 7 mm.; of the xiphiplastron, 5 mm. In front of the hyoplastra there was 

 probably a small fontanel, indicated by a notch in each bone. The notch farther from the 

 midline received one end of the entoplastron. The lower surface of all the plastral bones is 

 covered with shallow pits. Most of these are in rows parallel with the tree borders of the 

 plastron. There are four, sometimes five, sometimes only three pits in a line 10 mm. long. 

 Mr. Walter Granger, in 1903, discovered at Grizzly Buttes the skull and the outer end of 

 the left hypoplastron of a trionychid which proves to belong to the present species. Judging 

 from the portion of hypoplastron, the individual was about half-grown. The specific identity 

 of this bone with that of the larger individuals is furnisht bv a hypoplastron belonging to the 

 Cope collection. No. 1030 of the American Museum of Natural History. Of the skull (figs. 

 633-635) practically all portions are represented; but the palatal region has not been cleaned 

 of the matrix. The premaxillary bone is wanting and the occipital condyle is broken away, 

 but the length of the skull from the extremity of the one of these bones to the other has been 

 close to 50 mm. From the snout to the end of the supraoccipital process has been 57 mm. 

 The head is narrow, 24.5 mm. wide, slightly less than one-half the length to the occipital 

 condyle. The snout is long and narrow. The upper surface of the skull forms a regular 



6^4. 

 FlGS. 632-625. Plastomenus thomasi. Plastron and skill 



&33- 



632. Plastron. Xj. No. 6018 A. M. X. H. 

 634. Skull, side view. Xi. No. 6015 A. M. N. H. 



633. Skull, upper view. X 1. No. 6015 A. M. N. H. 

 635. Lower jaw, from below. Xl. No. 6015 A. M. N. H. 



curve from the snout to the end of the supraoccipital process. The orbit has an antero-postenor 

 diameter of 10 mm., and the space between this and the nostril was the same. No postfrontal 

 bone has been discerned. The postorbital process of the jugal reaches the parietal and this 

 bone enters into the formation of the orbit, a very unusual arrangement. In Platypeltis 

 fpinifera the postfrontal bone is small, but it excludes the parietal from the orbit. In Plasto- 

 menus thomasi the interorbital space has a width of 4 mm. The squamosal process was 

 formed as in Platypeltis. The lower jaw (fig. 635) is narrowed in front; the symphysis is 14 

 mm. long. 



The respects in which this species differs from P. visendus, referred in a former publication 

 to /\ thomasi, will be given under P. visendus. 



Plusto 



ni'tnts tlihm 



Plastomenus visendus sp. nov. 

 Plate 87, figs. 1, z; text-figs, 636, 637. 



'"i. Hay, Amer. Geologist, xxxv, iqo6, p. 334, figure. 



Among the materials included in the Cope collection now in the American Museum of 

 Natural History there was found a cigar-box of fragments which had been collected in the 

 Bridger deposits of the Rattlesnake Hills, Wyoming, in 1895, by Mr. Stanley Stuart. On 

 being fitted together these fragments furnisht a nearly complete carapace and plastron of a 



