474 FOSSIL TURTLES OF NORTH AMERICA. 



The free borders of the costals are thick and obtuse, resembling the edge of one's little 

 finger (plate 86, fig. 6b). That costal which forms the lower part of fig. 6 here presented has a 

 thickness of 12 mm. The upper surface of the costals is ornamented with pits, of which there 

 are about 4 in a line 10 mm. long, being somewhat larger than stated by Cope. On what are 

 evidently posterior costals there are conspicuous welts, which, at the distal ends of the costals, 

 run parallel with the sutural borders. The pits are in rows parallel with the free borders of 

 the costals. 



The portion of the hypoplastron belonging to the type agrees closely in form with that of 

 P. thomasi. Cope's figure is reproduced on page 86, fig. 8. The lower border joined the hypo- 

 plastron. The lower half of the border on the left joined the hyoplastron of the opposite side. 

 The oblique border above this formed a part of the boundary of a fontanel. The lower sur- 

 face, as seen, was sculptured with pits, arranged in rows parallel with the mesial border. These 

 pits are smaller than those of the carapace, there being about 6 or 7 of them in a 10 mm. line. 



In his description given in the Wheeler Survey Cope includes some fragments in this 

 species that he afterwards (Vert. Tert. Form. West, p. 125) referred to P. molopinus, the type 

 of which came from the Bridger beds. While these specimens quite certainly do not belong 

 to P. commums, it is doubtful if they belong to P. molopinus. It is to be noted that in the 

 text of the Wheeler Survey Cope refers to these specimens as representing a "var. ii," but in 

 the explanation of his plate xxv he speaks of them as "var. i." 



Plastomenus thomasi Cope. 

 Text-figs. 633-637. 



Trionyx thomasit, COPE, 1872, Proc. Amer. Philos. Soc., XII, p. 462. 



Plastomenus thomasii, COPE, Proc. Acad. Nat. Sci. Phila. 1873, P- 2 7^ (name only); 6th Ann. Report 



U. S. Geol. Surv. Terrs., 1872 (1873), p. 618; Ann. Report Chief Engineers, 1875, Append. LL, p. 



1016 (of reprint, p. 96.) HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 453. 

 Plastomenus multifoveatus, COPE, 1873, Proc. Acad. Nat. Sci. Phila. p. 278 (name only); 6th Ann. 



Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 619; Vert. Tert. Form. West, 1884, pp. 123, 125, 



plate xviii, figs. 2-8. 



The original description of the present species was extremely brief; and we could only 

 with difficulty know that it applied to the species, had not Professor Cope quoted it in subse- 

 quent and more detailed descriptions. Only portions of the carapace were mentioned. What 

 appears to be the next reference to the species, that in the Proceedings of the Philadelphia 

 Academy, was accompanied by no characters to distinguish it from related species. With it 

 was mentioned another species called P. multifoveatus. It was in this communication that the 

 genus Plastomenus was proposed, the characters of which were based on both carapace and 

 plastron. In Hayden's Report for 1872, as cited above, there appear descriptions of both P. 

 thomasi and P. multifoveatus. With the former were briefly described some plastral bones. 

 In the fourth volume of the Wheeler Survey, Professor Cope described New Mexican specimens 

 which he regarded as belonging to P. multifoveatus. To this species he now refers the 

 specimens which he had originally called P. thomasi, while the latter name is restricted to 

 plastral bones which he states were more like those of Trionyx. In the Vertebrata of the 

 Tertiary Formation of the West, 1884, he writes as follows under P. multtfoveatus: 



When I stated there [Report Geol. Surv. 1872] that P. thomasii is the type of the genus Plastomenus 

 I referred to these specimens; it is therefore to be observed that the type of the genus is really the P. 

 multifoveatus. The true P. thomasii was founded on sternal bones perhaps of a small species oCTrionyx. 



Regarding this statement the following may be said: (i) No plastral bones were men- 

 tioned in the original description of P. thomasi. (2) The description of P. thomasi found in 

 the Hayden Survey report of 1872 was taken bodily into the description of 1884. (3) We 

 know of no description of the plastral bones on which Cope says that P. thomasi was founded. 

 In view of these facts we must say that whatever Cope had in mind, he did not, according to 

 the recognized rules of nomenclature, attach the name P. thomasi to the Trionyx-like plastral 

 bones, but did attach it to those specimens which he afterward called P. multifoveatus. The 

 latter name therefore becomes a synonym of the former. 



