528 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Breadth, 14.5 mm., or more; length, 8 to 8.5 mm. Radiating- striae from 

 forty to fifty in number, often bifnrcating toward the anterior border, 

 crossed by numerous thread-like concentric striaj. Number of spines not 

 determined with certainty; two or three, perhaps more, on either side of 

 the beak. 



There can be no difficulty in distinguishing this species from C. logan- 

 ensis, even where both occur in the same beds. It is somewhat smaller, 

 more coarsely striate, and very much more gibbons. The alation also is 

 more striking and forms a characteristic feature. 



The smaller type of C. ornatus has sometimes been confused with C. 

 logani var. aurora Hall; but the surface ornamentation of the latter is very 

 distinctive. 



I venture to predict that this species, or at least the form from the 

 Chouteau limestone, will be found to be the same as G. logani Norwood and 

 Pratten. 



Formation and locality : Madison limestone, east side of Gallatin River, 

 west of Electric Peak; Crowfoot Ridge, Gallatin Range, bed 25; J. P. 

 Ridings and G. M. Wright. South slope of Quadrant Mountain, Gallatin 

 Range ; A. C. Gill. South base of same ; cherty belt, Bighorn Pass, Gal- 

 latin Range ; J. P. Iddings. Crowfoot Ridge, Gallatin Range, bed 24 ; 

 A. C. Gill. North of Owl Creek, northeast slope of Teton Range; W. H. 

 Weed. Limestone bluff south side of Soda Butte Creek, northwest of 

 Abiathar Peak, Absaroka Range; J. P. Iddings. Chouteau limestone, 

 Louisiana and Hannibal, Missouri. 



PRODUCTELLA Hall, 1867. 



Productella cooperensis Swallow. 



PL LXVIII, figs. 8a, 8b, 8c, 9a, 9b. 



Productus cooperensis Swallow, 1860: Trans. St. Louis Acad. Sci., Vol. I, p. 640. 

 Wiuchell (A.), 1865: Proc. Acad. Nat. Sci. Philadelphia, p. 115. 



Shell small. Ventral valve strongly arched, beak rather produced 

 and incurved. Ventral valve slightly concave or subplane over the vis- 

 ceral region and more or less sharply geniculate near the margin. Sur- 

 face marked by nearly obsolete spiniferous ridges and by strong concentric 

 wrinkles, especially noticeable about the posterior portion and near the 



