STANTON.] AVICULID^E. 79 



neat little species, both valves of which, in a majority of cases, are to- 

 gether in their natural position. 



" Position and locality. — Strata of the Cretaceous period; Ojo del 

 Piscado, New Mexico." 



This species is common at the base of Mesa Verde, near Mancos, Colo., 

 where it occurs in the Colorado formation about 400 feet above its base, 

 associated with Prionocyclus macombi and Ostrea lugubris. Some ex- 

 amples are much larger than the type, measuring 5 cm . in length. All 

 the larger specimens are irregular and distorted in shape and with an 

 almost smooth surface excepting near the beaks. 



Inoceramus simpsoni Meek. 



PL xn, Fig. 1. 



Inoceramus simpsoni Meek, 1860, Proc. Acad. Nat. Sci., Phila., p. 312; 1876, Simp- 

 son's Expl. across Great Basin of Utah, p. 360, PI. 4, Fig. 4; 1877, U. S. Geol. 

 Expl. 40th Parallel, vol. iv, pt. 1, p. 142, PI. 13, Fig. 4; Whitfield, 1880, Geol. 

 Black Hills of Dakota, p. 395, PI. 8, Fig. 1. 



Meek's description : 



"Shell (right valve) attaining a rather large size, transversely oval- 

 suboblong, gibbous, the greatest convexity being in the antero-central 

 region, cuneate posteriorly; length nearly twice the height; anterior 

 end very short and rounded from the beaks; base forming a long, semi- 

 elliptic curve, most prominent near the middle and somewhat straight- 

 ened, or even slightly sinuous, posteriorly; hinge-line long, straight, 

 and ranging parallel to the longer axis of the shell; posterior margin 

 sub truncated, with a slight backward slope above, and forming an 

 abrupt curve into the oblique posterior basal margin; beaks depressed 

 so as to project a little above the hinge line, incurved, and placed nearly 

 over the anterior margin. Surface ornamented with moderately dis- 

 tinct, regular, concentric undulations and lines of growth. 



"Length, 8.10 inches; height, about 4.30 inches; convexity of right 

 valve, nearly 2 inches." 



Locality and position. — The type specimen, and the only one that 

 Meek examined, comes from " North Platte river, above Platte bridge, 

 in Dakota Territory, from the Cretaceous formation No. 2 or 3 of the 

 upper Missouri section." The Dakota examples described by Whitfield 

 are from the Old Woman fork in the Fort Pierre group, and from the 

 east fork of Beaver creek, in probably the Fort Benton. 



Inoceramus gilberti White. 



PI. xiv, Figs. 3 and 4. 



Inoceramus gilberti White, 1876, Geol. Uinta Mts., p. 113; 1879, 11th Ann. Rept. U. S. 

 Geol. Sur.Terr., p. 285, PI. 3, Figs. 1 a, o, c. 



The revised description is as follows: 



" Shell irregularly suboval in marginal outline, the transverse diam- 

 eter being greater than the vertical; front more or less flattened; valves 



