TESTUDINIDA. 405 
the lip is 23 mm.; at a point halfway to the axillary notch this thickness is reduced to only 
21 mm.; near the notch it is about 10 mm. Superiorly the lip extends back about 50 mm. 
From the summit of the lip two ridges, with a shallow valley between them, run toward the 
axillary notch, diverging gently. There was evidently no thoracic excavation in the hinder 
face of the lip. 
The posterior lobe (fig. 628) was broadly notcht behind, the notch having a width of about 
go mm. and a depth of 35 mm. The terminal lobules are directed outward and upward, ear- 
like, somewhat as they are in Gopherus polyphemus, but not so narrow as they are in the latter. 
From the midline behind, the border is acute around the lobules and as far forward as about 
35 mm. behind the hypoxiphiplastral suture. Here it rather suddenly becomes broadly rounded 
as shown by the cross-section (fig. 628a). At the suture mentioned the thickness of the bone 
is 30mm. The wall thus formed continues backward, descending somewhat, and meets the 
6274. 
628a. 
627. 628. 628). 
Fics. 627 aND 628.—Testudo atascose. Plastron of type. 4. 
627. Anterior lobe; a, section of epiplastral symphysis. 
628. Hinder lobe; a, section at hypoxiphiplastral suture; b, at extremity of xiphiplastron. 
midline 15 mm. or more in front of the bottom of the notch. Fig. 6284 presents also a section 
thru one of the lobules in a direction from its tip toward the center of the hinder lobe. The 
greatest thickness is 22 mm. 
The femoro-anal sulcus runs from the midline outward, so as to make the outer end of the 
anal scute somewhat wider than the mesial end. Antero-posteriorly, at the middle of its width, 
the scute is 40 mm. long. 
The deposits in which this tortoise was found belong to the Equus beds of the Pleistocene. 
In the same region Mr. Marnock collected Terrapene marnochi (Cope) and Trachemys 
bisornata (Cope) (Proc. Amer. Philos. Soc., xvi, 1878, pp. 228, 229; Amer. Naturalist, 
xxi, 1889, p. 161). 
It is not improbable that this species belongs to the genus Gopherus. 
Superfamily TRIONYCHOIDEA. 
Thecophora with skull and neck in all essential respects like the same parts in the Crypto- 
dira. Horny jaws concealed beneath fleshy lips. Peripheral bones rarely present. Plastron 
ligamentously connected with the carapace. Epiplastra separated from the hyoplastra by the 
entoplastron. Pelvis not suturally connected with the carapace and plastron. So far as known, 
no epidermal scutes. 
Of the Trionychoidea, 2 families are here recognized—the Trionychide and the Plasto- 
menida. The former family is represented by numerous living species; the latter is extinct. 
In his Bibliography and Catalogue of the Fossil Vertebrata of North America, constitut- 
ing Bulletin No. 179 of the U. S. Geological Survey, publisht in 1902, the author regarded 
30 
