4.86 FOSSIL TURTLES OF NORTH AMERICA. 



KEY TO THE SPECIES OF ASPIDERETES. 



A 1 . Judith River and Laramie species: 



1. Shell of moderate size, broad; middle region of carapace with round pits, somewhat 



scattered; distal ends of costals crossed by furrows and ridges; plastron with 



twisted ridges foveatus 



2. Shell large, broader than long; pits numerous everywhere, in rows across distal ends 



of costals; nuchal excavated in front coalescens 



3. Shell large, considerably broader than long; sculpture like that of coalescens, 



but less in rows across outer ends of costals; nuchal convex in front, straight 



behind splendidus 



4. Shell nearly as broad as long, sculpture of carapace as in coalescens; nuchal straight 



or convex in front, shorter from side to side than splendidus; sculpture of plastron 



finer than in coalescens beechen 



5. Nuchal with thick abrupt free border; its width equal to half the distance from pre- 



neural to outer end; thickness at preneural border of type 4 mm.; pits not large. . . fontanus 



6. Nuchal with thick abrupt free border; width probably less than in A . fontanus and 



thickness greater; pits large and irregular in arrangement austerus 



7. Nuchal three-fifths as wide as distance from preneural to outer end; free border 



beveled off; bone at preneural border 7 mm. thick, preneural as wide as nuchal. . vorax 

 A 2 . Arapahoe species: 



A species not well known. Pits of costal bones shallower than in the species numbered 



2, 3 and 4, and with less abrupt walls vagans 



A 3 . Fort Union and Puerco species: 



1. Disk of carapace longer than wide; nuchal joined by its whole length to preneural 



and first costals; the outer end hardly reaching the rib of the first costal; 5 to 7 



pits in 25 mm. line sagatus 



2. As in sagatus, but the outer end of the nuchal extending across the rib of the 



first costal; 6 to 8 pits in a 20 mm. line on proximal ends of costals; only 3 or 4 



on distal ends singularis 



3. Disk wider than long; sculpture obscure in known specimen, but finer than in 



sagatus nassau 



4. Disk longer than wide; nuchal loosely joined to preneural and costals; fontanels 



behind it puercensis 



A*. Bridger species: 



1. Preneural doubtfully present; a fontanel on each side of its position. Pits of cara- 



pace large guttatus 



2. A well-developed preneural and no fontanels; sculpture somewhat coarser than in 



either the preceding or the following species; second and third neurals about 



half as wide as long ellipticus 



3. A well-developt preneural and no fontanel; sculpture like that of guttatus; second 



and third neurals nearly two-thirds as wide as long grangeri 



Aspideretes foveatus (Leidy). 

 Plate 89, figs. I, 2; teit-figs. 643, 644. 



Trionyx foveatus, LEIDY, Proc. Acad. Nat. Sci. Phila. vin, 1856, pp. 73, 312; Amer. Jour. Sci., (2) 

 xxn, 1856, p. 120; Trans. Amer. Philos. Soc., xi, 1860, p. 148, plate xi, figs. 1-3. COPE, Synop. 

 Ext. Bat. Rept. and Aves N. A., in Trans. Amer. Philos. Soc., xiv, 1869, p. 152; Bull. U. S. Geol. 

 and Geog. Surv. Terrs., I, 1879, No. 2, p. 29; Vert. Tert. Form. West, 1875, p. 260; Bull. U.S. 

 Geol. and Geog. Surv. Terrs., 1877, in, p. 573. LAMBE, 1902, Geol. Surv. Canada, Summary 

 Rept. for 1901, p. 81, plates i, ii; Cont. Canad. Palaeont, in (4 to), pt. II, p. 33, plate i, figs. I, 2, 

 text-fig, i. HAY, Bibliog. and Cat. Foss. Vert. N. A., p. 454, 1902. HATCHER, Bull. U. S. Geol. 

 Surv. No. 257, 1905, p. 72. 



The specimens described by Dr. Leidy under the name Trionyx foveatus were collected by 

 Dr. F. V. Hayden partly in the Judith River beds of Montana and partly in beds supposed to 

 be of the same age, near Long Lake, in what is now Burleigh County, North Dakota. 



Those from the Judith River basin are described as consisting of small fragments of costal 

 and sternal plates; and of these the proximal half of a costal plate and two fragments of a 

 hypoplastron are described and figured in Leidy's paper of 1860 on "The Extinct Vertebrate 



