white.] PALEONTOLOGY — CRETACEOUS FOSSILS. 285 



Position and locality. — The original examples were collected by Mr. E. 

 E. Howell from Cretaceous strata in Lower Potato Valley, Southern 

 Utah. I afterward discovered some imperfect examples in strata of the 

 Pox Hills Group, near Captain Dodds's ranch, in the valley of Ashley's 

 Fork, Utah. 



Inoceramus gilberti White. 



Plate 3, figs. 1 a, b, and c. 

 Inoceramus gilbeiii White, 1876, Powell's Eep. Geol. Uinta Mts. p. 113. 



Shell irregularly suboval in marginal outline, the transverse diameter 

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

 nearly or quite equal, the left one, if either, the larger, both of them gib- 

 bous, and sometimes quite ventricose ; umbones broad and elevated ; 

 beaks very near the front, incurved, but not projecting beyond the front 

 margin ; front nearly straight vertically, or sometimes more rounded, in the 

 former case forming nearly a right angle with the hinge ; front margin 

 rounded below to the basal margin, which is broadly convex for more 

 than half the .length of the shell ; postero-basal margin extending ob- 

 liquely upward, with a slight emargination, to the posterior extremity, 

 which is abruptly rounded to meet the downward-sloping postero-dorsal 

 margin ; dorsal margin straight, its length equaling more than half the 

 long diameter of the shell. Upon each valve there is an obscure radiating 

 depression, or ill-defined furrow, extending from the umbonal region to 

 the postero-basal border, and ending there at the emargination before 

 mentioned. 



Surface marked by the usual bines of growth, and also by numerous 

 extravagant, irregular concentric folds or wrinkles. 



This species belongs to a section of the comprehensive genus Inocera- 

 mus that Brongniart designated under the name Catillus. It is a pecu- 

 liarly well-marked species, and readily distinguishable from any other 

 published species from American strata. 



Transverse length of an average-sized specimen, 7£ centimeters ; height 

 from base to hinge, 5 centimeters. 



Position and locality. — Cretaceous strata, probably of the Fox Hills 

 Group ; near Last Chance Creek, Southern Utah, where it was collected 

 by Mr. G. K. Gilbert. 



Inoceramus oblongus Meek. 



Plate 2 ; figs. 1 a and b. 

 Inoceramus oMongns Meek, 1871, An. Rep. U. S. Geol. Surv. Terr, for 1870, p. 297. 



Shell large, inflated, longitudinally oblong or suboval in marginal out- 

 line, widest near the posterior end ; valves nearly or quite equal ; hinge- 

 line long and straight ; posterior margin long, broadly convex, subtrun- 

 cating the shell obliquely downward and a little backward; front and 

 basal margins forming a continuous but unequal curve, being greatest 

 in front and least near the postero-basal region ; beaks equal, not very 

 large, nearly terminal, raised above the hinge-line, incurved, and point- 

 ing very little forward. Test comparatively thin for so capacious a 

 shell. 



Surface marked by the ordinary lines of growth, and usually by more 

 or less distinct concentric undulations. 



Tin's shell bears some resemblance to I. oarabini Morton, but it is a 

 much larger and more gibbous shell, the adult examples becoming ex- 



