6 9 6 NORTH AMERICAN INDEX FOSSILS. 



Coal measures of Illinois, Iowa, and Missouri. 



291. A. stevensana M. and W. (Fig. 999.) Carbonic. 

 Minute, 6.5 mm. long, rather slender, deep-sutured, with 5 or 6 



strong, slender, and distant spirals, the lower generally covered, 

 except in the body whorl. 



Coal measures, Illinois, Missouri, and New Mexico. 



292. A. minuta Stevens. Carbonic. 

 Minute, slender, deep-sutured, of nine or more volutions ; aper- 

 ture subcircular ; surface with numerous fine spirals. 



Coal measurers of Illinois, Iowa, and Missouri. 



LXXXIII. Orthonema M. and W. 

 Whorls more or less angulate and marked by a few revolving 

 spirals. Otherwise as in preceding. Carbonic. 



293. 0. conicum M. and W. (Fig. 1000.) 



Carbonic. 

 Small ; whorls flattened, angulated below ; sutures 

 moderately deep ; spirals three, very faint, the lower 

 below angulation, covered except in body whorl. 

 Fig. 1000. Coal measures of Iowa and Illinois. 



Orthonema 



conicum. 2 94- 0. subtaeniatum Geinitz. Carbonic. 



(After Meek With three subequally spaced revolving carinae, 



and Worthen, th lower Qne covered in all but the body w horl. 

 111. V. ) J 



Coal measures of Iowa, Nebraska, etc. 



Family Subulitid^e Lindstrom. 



LXXXIV. Subulites Conrad. 



Thin, slender, subulate or fusiform shells, with high, flat, or 



slightly convex whorls, faintly impressed suture, elongate narrow 



aperture, acuminate above and wider or somewhat truncate below, 



with lip strongly recurved. Surface smooth. Ordovicic. 



295. S. elongatus Conrad. Ordovicic. 

 Six or more flattened or very gently convex volutions ; spire 



tapering gently, body more rapidly enlarging. 

 Trenton of New York, Canada, etc. 



296. S. regularis U. and S. (Fig. iooi, a.) Ordovicic. 

 Large ; more slender than preceding ; eight or ten whorls, rapidly 



contracting in lower half of body whorl. 



