144 UNITED STATES GEOLOGICAL SURVEY OF TD.E TERRITORIES. 



more rounded posterior extremities; the beaks are also located propor- 

 tionally farther back. 



It is a remarkable and interesting fact that this, the first of the species 

 believed to belong to this genus discovered in America, is found in a Creta- 

 ceous rock associated with a Baculite ; while all the known congeners in the 

 Old World occur in the Lias and Lower Oolite. 



Locality and position. — Mouth of Judith River, on the Upper Missouri, 

 in a Cretaceous bed holding a position in the very upper beds of the Fox 

 Hills group. The occurrence of this type at this locality, at one time, gave 

 origin to the suspicion that these beds might be of Jurassic age; but later 

 collections show that Baculites and other decided Cretaceous types occur 

 directly in the same association. 



Since the above was in type, Dr. Hayden has brought this species from 

 a locality on Cache La Poudre River, in Colorado, where it occurred asso- 

 ciated with other species found at the Upper Missouri locality.* 



GLOSSIDiE.t 

 Genus CYPRINA, Lamarck. 



Synon.—Cyprina, Lam. (1812), Extr. d'uu Cours., * * ; and (1818), Hist. Nat., V, 556 (2e eel.), VI, 287 — 

 Ferass. (1821), Tab. Syst., xliv.— Blamv. (1825), Malac, 552.— Desh. (1830), Encyc. 

 MeSth., Ill, 45.— Agassiz (1839), Moul. d. Moll., 36.— Reeve (1841), Conch. Syst., I, 90.— 

 G. B. Sowerby, jr. (1842), Conch. Man. (2d ed.), 134.— Geiuitz (1846), Gr. d. Verst., 436; 

 and of numerous others. 

 Arctica, Sebum. (1817), Ess., 145. 



Etym. — Kv-rrpie, a name of Venus. 

 Type. — Venus Islaiidhttu, Linn. 



Shell transversely oval or suborbicular, inequilateral, solid, generally 

 rather convex ; free margins closed, and smooth within ; surface concentrically 

 striated, and covered with a dark, thick, corneous epidermis; ligament 

 prominent, and attached to strong fulcra; beaks obliquely, but not very 



* In giving the locality and position of the other species from this same horizon in the Upper 

 Missouri, on some of the preceding pages of this work, it is merely stated that tbey came from Cretaceous 

 beds, the exact horizon of which remained undetermined. While these pages are going through the 

 press, Dr. Hayden's collection of the past summer (1874), in Colorado, have just come in, and tbey show, 

 as above intimated, that this formation is well developed there, on Cache La Poudre River, west of 

 Greeley, where it is intimately associated with the upper beds of the Fox Hills group. 



t Since seeing the illustrations of the genus Veiiithcardia, Stoliczka, and some other intermediate 

 extinct forms, I am led to follow Deshayes and Dr. Stoliczka in including the genus Cyprina and its 

 allies with Glossus (= Isoeardia) iu the one family, for which Dr. Gray's name Glossida: may be retained. 

 Like Dr. Stoliczka, however, I am very far from agreeing with Deshayes iu including Cardium in the 

 same family. Yet Dr. Stoliczka also includes iu it several genera that seem to me to belong to distinct 

 families. 



