718 GEOLOGICAL SURVEY OF IOWA. 



GASTEROPODA OF THE COAL MEASURES. 



Among the fossils of the Coal measures as developed in 

 the valley of the Mississippi and to the eastern limits of 

 Ohio, we find a greatly increased number of Lamellibran- 

 chiata and Gasteropoda. The latter, in the Genera PLEUROTO- 

 MARIA, MACROCHEILUS, BELLEROPHON, and other forms, are every 

 where common, and in some of the strata not unfrequently 

 abundant. Associated with these are likewise numerous forms 

 of the Cephalopoda of the Genera NAUTILUS, GONIATITES, and 

 ORTHOCERAS ; but it has been impossible, for want of space, 

 to illustrate these genera in the present volume. 



Macroclieilus lusiforinis ( n. s.). 



PLATE XXIX. FIG. 7. 



SHELL elongate, subfusiform. Spire gradually tapering from 

 the last volution which is more ventricose, consisting of 

 seven or more volutions, which are very moderately convex 

 except the last. Suture-line faint in the shell, deeply ca- 

 naliculate in the cast : aperture not fully known, nearly 

 equalling half the length of the spire. 



This shell corresponds in general form and characteristics with M. missourensis 

 of SWALLOW; but the angular character of the volutions in the cast is not observed. 



Fig. 7. View of a specimen (of the natural size), from which the shell is partially 

 exfoliated, and several of the volutions at the apex broken off. 



Geological formation and locality. Coal measures : Alpine dam, Des- 

 nioines valley, Iowa. 



Macrocheilus ventricosus ( n. s.). 



PLATE XXIX. FIG. 8. 



SHELL ovoid -acute : last volution very ventricose, and 

 more than twice the length of the spire above, which rapidly 

 tapers to an acute apex. Volutions moderately convex, about 

 eight or more altogether ; columellar lip thickened. 



