300 EEPORT UNITED STATES GEOLOGICAL SUEVEY. 



but not turned forward ; a distinct sulcus radiates from just behind each 

 of the beaks toward the postero-dorsal margin, but becomes obsolete 

 before reaching it. These sulci give the back of the shell a hollowed ap- 

 pearance behind the beaks. Another hnear depression, but a faintly 

 defined one, extends from the posterior side of the beak to the obtuse 

 postero-basal angle of the shell, its position being immediately behind 

 that of an umbonal ridge, if one existed. 



Surface marked by the usual lines of growth and also by strong con- 

 centric wrinkles, which latter are a little stronger in front of than behind 

 the faintly defined umbonal depression before mentioned. 



Length, 85 millimeters ; height fr-om base to beaks, 53 millimeters ; 

 thickness, about 34 milhmeters. 



The hinge of this species has not been seen, but the external char- 

 acteristics of the shell are so in keeping with those of the typical forms 

 of Glycimeris as to leave no doubt that it is x>roperly referable to that 

 genus. Indeed, it bears considerable resemblance to 3£ya glycimeris, 

 Lamarck's type of the genus ; but it differs from that species in the 

 greater proportionate height of the shell behind the beaks, the great 

 length of the j)osterior border and its downward and forward truncation 

 of the shell, the angular character of the postero-ventral border, &e. 

 Our type-specimen is very like one in the cabinet of the Smithsonian 

 Institution labeled " From near Marlboro, IsT. J.," and which probably 

 belongs to the Fanopcea decisa of Conrad; but the hinge-line of our 

 species is straighter, and both the antero and iDostero-dorsal portions 

 are more elevated and more compressed. The only other American 

 species with which it need be compared is G. occidentalis Meek & 

 Hayden, vol. ix (4to series), U. S. Geol. Surv. Terr., p. 250, pi. 39, figs. 9 a 

 and b ; but it differs from that species in the i^eculiar posterior trunca- 

 tion before mentioned, the greater proportionate length of the hinge- 

 margin, and the greater prominence and elevation of the antero-dorsal, 

 as well as of the postero-dorsal i^ortion. The specific name is given 

 in honor of Oapt. E. L. Berthoud, of Golden City, Colo., to whom the 

 Survey is indebted for interesting fossUs and many accurate observa- 

 tions, the result of his large experience in the Eocky Mountain region. 



Position and locality. — Strata apparently equivalent with Cretaceous 

 Ko. 3, or Fort Pierre Group of the Upper Missouri section ; about 15 

 miles west of Greeley and about 6 miles south of Fort Collins, Colo. 



Genus PAEAPHOLAS Conrad. 



Paeapho.las sphenoideus White. 



Plate 5, figs. 1 a, h, c, and d. 



Twmus spZicnoidews White, 1876, Powell's Eep. Geol. Uinta Mts., p. 117. 



Shell elongate, cuneate, inflated in front, narrowed and laterally com- 

 pressed behind ; beaks anterior, incurved, adjacent ; dorsal margins of 

 the valves straight and sloiiing from the beaks to the posterior end, 

 capped or connected by a slender, styliform, x>lain, accessory plate; 

 posterior extremity small, truncated, or narrowly rounded ; basal mar- 

 gins nearly straight, connected by a ventral accessory plate similar to 

 the dorsal one, except that it is shorter, broadest behind, but coming to a 

 slender \iomt in front about midlength of the shell longitudinally, 

 divided by a hnear groove ; front regularly rounded, both vertically and 

 laterally ; anterior gape consisting of a narrow, vertical slit, which occu- 

 pies the middle of a somewhat ijrominent jjrojection at the antero-basal 



