trionychida:. 



537 



3. Carapace oval, not so wide as long, archt; nuchal about half the width of cara- 



pace; pits of com. ils small and shallow; hinder end of carapace with longitudinal 



welts trionychoides 



4. Carapace as broad as long; nuchal hardly half the width of the carapace; a 



smooth band along its front; sculpture coarse near midline heteroglypta 



5. Cat apace broader than long; nuchal more than half the width of carapace; 



pitted to free bonier; sculpture as in preceding postern 



6. Carapace broader than long; nuchal not half the width of the carapace; 



sculpture like that of heteroglypta extensa 



A . < Higocene species: 



1. Carapace thin, broader than long; nuchal 0.6 the width of the carapace; a 



fontanel each side of first neural leucopotomica 



A . Pliocene and recent species: 



i. Carapace elliptical; longer than wide; nuchal about half the width of the cara- 

 pace; sculpture rather coarse ferox 



Platypeltis antiqua Hay, 

 Fig. 693. 



Platypeltis antiqua, Hay, Bull. Amer. Mus. Nat. 

 Hist., win, 1. 107, n. 859, fig. 18. 



The specimen which represents this species 

 appears to have been collected for Professor 

 Cope by Mr. D. Baldwin, in 1883, in the 

 Torrejon beds of northern Mexico. It pre- 

 sents wholes or parts of 5 pairs of costals and 

 5 neural bones. Some other bones are buried 

 in the very refractory matrix. The catalog 

 number is 1036. 

 The carapace 

 (fig. 693) had a 

 length of about 

 100 mm. and a 

 width of 78 mm.; 

 but the ends of 



the ribs extended beyond the disk at least 18 

 mm. What is evidently the first costal is 20 

 mm. long, from neural to distal end, and 13 

 mm. fore and aft. Its anterior border is smooth, showing that it was not suturally joined to 

 the nuchal. The table shows the dimensions of the neurals present. They are from 2.5 mm. 

 to 3 mm. thick. 



The surface of the costals presents no w r elts, but is everywhere pitted. On the proximal 

 ends of the costals there are 6 pits in a 10 mm. line; on the outer ends, 5 pits. 



Fig. 693, 



-Platypeltis antiqua. 

 of type. X f 



,a rap ace 



Platypeltis serialis (Cope). 

 Plate 98, fig- 13; plate 104, figs. 1-4; text-figs 694-696. 



Trionyx, Leidy, Contrib. Ext. Vert. Fauna West. Terrs., 1873, p. 180, plate xvi, fig. II. 



Plastomenus fthomasii, Cope, Syst. Cat. Vert. Eocene, New Mexico, 1875, p. .55. 



Plastomcnus thomasii, Con , Wheeler's Surv. W. 100th Merid., iv, 1877, p. 49. (NotTrionyx thomasii 



Cope, 1872.) 

 Plastomenus thomasi, Cope, Vert. Tert. Form. West, 1884, p. 125. (Not Trionyx thomasii Cope, 1872.) 

 Plastomenus sennits, Cope, Wheeler's Surv. W. 100th Merid., iv, 1877, pp. 48, 51, pi. xxv, figs. 8-10; 



Vert. 'lett. form. West., 1884, p. 123. -Hay, Bibliog. and Cat. Foss. Vert. N. A., 1903, p. 455. 

 Platypeltis serialis, Hay, Amer. ( Icologist, xxxv, 1905, p. 337. 



The types of the present species appear to have been lost. We must, therefore, depend 

 for the identification of the species on the author's description and illustrations. Professoi 

 Cope possest fragmentary remains of five individuals, which he had obtained from the Wasatch 



