142 PALEONTOLOGY. 



PTEEIID^. 



Genus INOCERAMUS, Sowerby. 

 Inocekamus Simpsoni, Meek. 



Plate 13, fig. 3. 



Inoeeramus Simpsoni, Meek (1860), Proceed. Acad. Nat. Sci. Pbilad., XII, 312 ; and 

 (1876) iu Ool. Simpsou's Eeport Expl. across the Great Basiu of Utah, 360, pi. 

 iv, fig. 4. 



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

 long, 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 straightened, or even slightly 

 sinuous, posteriorly; hinge-line long, straight, and ranging parallel to the 

 longer axis of the shell; posterior margin subtruncated, with a slight backward 

 slope above, and forming an abrupt curve into the oblique posterior basal 

 margin; beaks depressed so as to project little above the hinge-line, 

 incurved, and placed nearly over the anterior margin. Surface ornamented 

 with moderately distinct, regular, concentric undulations and lines of growth. 



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

 valve, nearly 2 inches. 



The only specimen I have seen of this shell is a cast of the interior of 

 the right valve, with some portions of the moderately thick fibrous shell 

 attached. It belongs to the group CatiUus, as most generally understood, 

 excepting in wanting the peculiar flexure near the cardinal margin; that is, 

 to the group composed of nearly equivalve (or, at any rate, not very strongly 

 inequivalve) shells, with a more or less elongated hinge, ranging nearly or 

 quite parallel to the longer axis of the valves, instead of having a shorter 

 hinge standing nearly at rightangles to the longer axis, as in the typical 

 forms of Inoeeramus, which latter are often decidedly inequivalve. Although 

 I have seen but the right valve of this shell, it is evident, from its moder- 

 ately gibbous, as well as transversely elongated form, that it does not belong 

 to the more inequivalve section of the genus. Its most remarkable charac- 

 ters are its transversely elongated, very inequilateral form; being proportion- 



