BTANTON.] aviculid^:. 83 



INOCERAMUS EXOGYROIDES M. & H. 



PI. xvii, Figs. 1 and 2. 



Inoceramus erogyroides Meek & Hay den, 1862, Proc. Acad. Nat. Sci., Phila., p. 26; 

 Meek, 1876, U. S. Geol. Sur. Terr., vol. ix, p. 46, PI. 5, Figs. 3a, b, c. 



Kevised description : 



"Shell rather large; left valve suborbicular, its height being a little 

 greater than its length from the anterior to the posterior side, very 

 gibbons; anterior and posterior sides rounded, and forming with the 

 base about three-fourths of a circle, the posterior curve being broader 

 than the other; cardinal margin comparatively short, and apparently 

 a little arched; beak large, elevated, gibbous, distinctly incurved and 

 directed obliquely forward, so as to bring its point near the anterior 

 margin; surface of cast smooth, or marked by obscure concentric un- 

 dulations. (Right valve unknown.) 



"Length from anterior to posterior margin, 5 inches; height, 5.50 

 inches ; convexity, near 3 inches. 



"No right valves of this species have yet been found; but, judging 

 from the gibbous character and involuted beak of the left valve, it is 

 probable that the right will be found to be much more compressed, so 

 as to make the shell very distinctly inequi valve. The lateral curvature 

 of the beak of the left valve, together with its general form, give it 

 much the appearance of some species of Exogyra, as viewed from the 

 inner side. Its aperture is transversely oval, the height being to the 

 length about as four to five. Remaining portions of the shell show it 

 to have been quite thick about the beak, and, as in other species, dis- 

 tinctly fibrous. 



"Specifically, this shell differs from the last in being much more de- 

 pressed and in having its left beak considerably less elevated and 

 directed much more obliquely forward, as will be seen by comparing 

 Fig. 3 a, PI. 5, with Fig. 2 b, PI. 4. It probably belongs, however, to 

 the Volviceramus group. 



" Locality and position. — Chippewa point, near Fort Benton, on the 

 upper Missouri; from the same horizon as the last." 



Larger collections will probably show that this is identical with I. um- 

 uonatus. 



Inoceramus tenuirostrattjs M. & H. 



PI. XVI, Figs. 3 and 4. 



Inoceramus tenuirostratus Meek & Hayden, 1862, Proc. Acad. Nat. Sci. Phila., p. 27. 

 Inoceramus tenuirostris Meek, 1876, U. S. Geol. Sur. Terr., vol. ix, p. 59, Fig. 5 in text. 



Eevised description : 



"Left valve very gibbous, subquadrate in outline; anterior margin 

 very short or vertically truncated, with a slightly convex outline, imme- 

 diately in front of the beak, and rounded into the base below; ventral 



