140 CARBONIFEROUS PERIOD. 



here described, one is known to exist in the Subcarboniferous limestone of 

 Washington County, Indiana ; B. BurUngtonensis occurs in the Subcarbonif- 

 erous strata at Burhngton, Iowa, and in Nevada; and Professor Swallow 

 has described one from the Subcarboniferous strata at Chester, Illinois, 

 under the name of Terebratula arciiata. which is so nearly like B. bovidens 

 tliat it is difficult to say wherein they differ. It has not thus far been dis- 

 covered in the Permian strata of America, but it is understood to occur in 

 strata of that period in Em-ope. The geographical range of B. bovidens is 

 from Ohio to Nevada, and. it has been discovered from base to top of the 

 Coal-Measure series of sti-ata. 



Position and locality. — Strata of the Carboniferous period : near Santa 

 Fe, N. Mex. ; a few miles south of Saint George, Utah ; and at the top of 

 Grass Mountain, Ely range, thirty -five miles north of Pioche, Nevada. 



MOLLUSCA VERA. 



Class CONCHIFERA. 



Order MONOMYAIUA. 

 Family PECTINID^. 



Genus AVICULOPECTEN McCoy, 1852. 

 Aviculopecten occidentalis Sliuinard. 



Plate XII, iig. 8 a and b. 



Pecten oceidentalis Shumard, 1855, Geol. Surv. Missouri, 207 (not Winchell, 1863). 

 Pecten Cleavelandiciis Swallow, 1858, Traus. St. Louis Acad. Sci., i, 184. 



Aviculopecten ?, Meek and Hayden, 1864, Palteont. Upper Missouri, 50. 



Pecten Missouriensis Geinitz, 1866, Carbou format, und Dyas iu Nebraska, 35 (not 



Shumard, 1855). 

 Aviculopecten occidentalis 1872, U. S. Geol. Surv. Nebraska, 191. 



Shell inequivalve, both ears well defined ; the cardinal border at nearly 

 right angles with the axis of the shell, and almost as long as its full antero- 

 posterior diameter; outline, exclusive of the ears, subovate. Left valve 

 more convex than the right ; anterior ear about as long as the posterior, 

 more convex, and a little more sharply defined from the body of the valve 



