128 FOSSIL TURTLES OF NORTH AMERICA. 



When this author's work (Synopsis of the Extinct Batrachia, Reptilia, and Aves of North 

 America) was issued in 1870, he described (pp. 105-234) both Osteopygis and Propleura 

 as possessing 10 pairs of costal plates. In the latter genus he included only the species 

 sopitus, his repandus being made the type of a new genus Catapleura, and his chelydrinus 

 being referred to Osteopygis. Cope concluded that there were 10 pairs of costals because he 

 found a pit, as if for a rib, in the second peripherals and supposed that he had found a pit in 

 each of the eleventh peripherals. 



In that portion of the Synopsis (pp. 235-252) which appeared in December, 1870, Cope 

 stated that as regards Osteopygis the ascription to it of 10 pair of costals was an error, the last 

 peripheral not having had a costal corresponding to it. As to Propleura, he adhered to his 

 previous opinion that it possest 10 pairs of costals. 



In 1875 Cope (Vert. Cret. Form. West, p. 257) had concluded that the possession by Pro- 

 pleura sopita of 10 pairs of costals was very doubtful; and this species, with platylornus and 

 his new erosus were referred to Osteopygis; while chelydrinus went to Catapleura. Cope 

 still believed that Osteopygis possest at least 9 pairs of costals. 



In 1882 (Proc. Amer. Philos. Soc., xx, p. 144) and again in 1884 (Vert. Tert. Form. 

 West, p. 112), Cope defined Osteopygis as having 10 pairs of costals and Propleura as having 

 9, statements directly opposite to those formerly made. 



The correction of Cope's errors regarding the number of costals in the species of this group 

 was made by Dr. Baur (Zool. Anzeiger, xiv, 1889, p. 42). He studied the very complete 

 specimen which has since served Dr. Wieland as the type of 0. gibbi; and from this he 

 concluded that there were only 8 pairs of costals, and that the pit in the second peripheral 

 was for the reception of a process of the hyoplastron. Baur examined also Cope's types of 

 the species of Osteopygis, Propleura, and Catapleura and concluded that there were no generic 

 differences among them. 



Baur's results respecting the number of costals have been confirmed by Wieland. Never- 

 theless, Wieland adopts Cope's genus Propleura. He holds that Propleura differs in having 

 costo-peripheral fontanels, conical rib-pits, and humeri grooved on their distal ends. 



So far as concerns the grooving of the distal articular ends of the humeri, the present 

 writer does not believe that enough is known about the humeri, not only of the species of the 

 group in question but of the "living species, to justify the use of the character proposed by 

 Wieland to separate genera. Among species of Testudo it is found that the distal end of the 

 humerus of many, perhaps of most, is smooth and rounded; but that of Testudo orthopygia 

 has a broad trochlear groove. 



ANALYSIS OF THE SPECIES OF OSTEOPYGIS. 



1. All the peripherals sutured to the costals (Osteopygis). 



A. Posterior peripherals emarginate; upper borders of peripherals not notcht by the 



rib pits; thickness of outer end of nuchal about one-eighth its width emarginatus 



A A. Posterior peripherals not emarginate. 



a. Outer end of nuchal about one-eighth the width in front ; upper borders of 



peripherals notcht by rib-pits gibbi 



aa. Thickness of outer end of nuchal about one-sixth its width in front; upper 



borders of peripherals not notcht by rib-pits robustus 



2. Peripherals 3 to 10 inclusive free from the peripherals (Propleura). 



A. Hinder peripherals angulated at end of sulcus chelydrinus 



AA. Hinder peripherals neither angulated nor emarginate. 



a. Rib-pits of eighth and succeeding peripherals flattened; one face or both notcht 



by rib-pits. The seventh at least two-thirds as wide as long. 

 b. Bones thick and heavy; thickness of distal end of first peripheral in its length 



3.5 times; only upper face of hinder peripherals notcht by rib-pits. .. erosus 



bb. Bones thinner, thickness of distal end of first peripheral in its length 

 4.4 times; both faces of upper border of hinder peripherals notcht by 



rib-pits borealis 



bbb. Bones thinner; thickness of first peripheral in its length 4. 4 times; rib-pits 



of sixth and seventh peripherals flattened; both faces of peripherals notcht platylomus 

 fid. Seventh peripheral only half as wide as long sopitus 



