38 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Genus INOCERAMUS, Sowerby. 



Synon. — Inoccramus (Soworby, MS.); Parkinson (1819), Trans. Geol. Soc, V, 59. — Sowerby (1823), Trans. 



Linn. Sue, XIII, 557 ; and Min. Conch., Ill, tab. 305.— Fcrussac (1821), Tab. Syst., xli ; 



and of numerous subsequent authors. 

 CaUllus, Brongniart (1822), in Cuvier and Brong.'s Descrip. Geol. of the Environs of Paris, 386. — 



Blainville (1825), Mai., 529, and others. 

 Myliloides, Brongniart (1822), Geol. Environs of Paris, 622. — Bronn (1838), Leth., GDI, 695 (snb- 



gen. Xnocer annus). 

 Actinoceramus, Meek (18G4), Check-List Cret. Foss. N. Am., 32 (subgen. Inoccr.). — Stoliczka (1871), 



Palasout. Iudica, III, 393. 

 ' Volmccramns, Stoliczka; ib., 394 (subgen. Inoccr.). 



Etym. — iff, strength, fiber; xepa/ioc, earthen ware ; perhaps from the resemblance of large fragments of 



the fibrous outer-shell layer to broken pottery. 

 Type. — Inoeeratims ('iir'uri, .Sowerby. 



Shell varying, according to the sections, from subcircniar to transversely, 

 obliquely, or vertically oval or oblong, inequilateral, gibbous, or more or less 

 compressed, with valves equal, subequal, or sometimes distinctly, or even 

 extremely unequal in convexity, as well as in the relative prominence of the 

 opposite beaks. Anterior margins without any defined byssal sinus in either 

 valve; posterior dorsal margins sometimes compressed and subalate. Inner 

 nacreous layer thin, extending to the margins of the valves; outer fibrous 

 layer thick and coarsely prismatic. Hinge straight or very rarely a little 

 arched, generally narrow, nearly or quite edentulous within,* ranging at 

 various angles to the longer axis of the shell, and crossed by numerous small, 

 regularly-arranged cartilage-pits. Surface concentrically undulated and 

 striated, or nearly smooth ; very rarely with radiating plications or costse. 

 Muscular and pallial impressions very obscurely marked.f 



This extensive group of extinct bivalves includes a large number of 

 species, presenting great diversities of form, size, and general appearance. 

 An attentive study of these various forms shows that they may be conveniently 

 arranged under the following sections or subgenera, most of which have been 

 named by others : 



1. inoceramus, Sowerby (typical). 



a. Shell vertically ovate or subquadrate, gibbous, and more or 

 less distinctly inequivalve; hinge short, and ranging at right angles to 



* Goldfass' figure of I. alatus (Petref. Germ., pi. cxi, fig. 3, c, d) seems to show in the right valve, at 

 or under the anterior extremity of the hinge, three short pits for small teeth in the other valve. 

 /. alriatus, Mantell, as figured by d'Orbigny (Takeout. Pr., Ill, pi. 4U">), also shows a tooth-like projection 

 al the anterior end of the hinge of the loft valve. 



1 1 have never seen any traces of the muscular or pallial impressions of this genus ; but according to 

 d'Orbigny, it lias one huge subcentral muscular scar in each valve, as in other groups of the AricuUJa. 



