22 IOWA ACADEMY OF SCIENCES. 



CONTRIBUTION TO THE FAUNA OF THE LOWER COAL MEASURES 

 OF CENTRAL IOWA. 



BY CHARLES R. KEYES. 



Among a large number of species recently discovered in the lower coal measures 

 near Des Moines are some hitherto unrecognized forms. The following are the 

 descriptions of three of the most important shells.* 



CHONETES L.55VIS. 



Shell small; much wider than long; transversely semi-elliptical; the cardinal 

 line as long as the greatest width of the shell, or often slightly extended beyond 

 the lateral margins. Ventral valve convex, with no indication of a mesial sinus;- 

 beak not promiaent; cardinal area rather narrow but well defined centrally, 

 becoming linear toward the extremities; foramen moderately wide; cardinal mar- 

 gin bearing from four to seven oblique spines on each side of the beak. Dorsal 

 valve flat or very slightly concave; with no mesial fold. Surface of both valves 

 apparently perfectly smooth; but under a magnifier it is seen to be marked by 

 numerous fine concentric strife, and more prominent, often somewhat imbricated, 

 lines of growth; these are sometimes crossed by fine nearly obsolete radiating 

 strias. 



Length 7 mm.; breadth 12 mm. 



This species is found in the superimposing black shales of coal No. 3 at Des 

 Moines; and is associated with Chonetes yw^oloha, Productus mnricatiis, and the 

 minute gasterpods mentioned elsewhere. The glabrate character, and the absence 

 of a mesial fold and sinus, as is constant in all eight of the specimens found, forms 

 a marked contrast with the associated congeneric forms, in which the radiating 

 striae are unusually sharp and well defined; and also with the other carboniferous 

 forms of the same genus. This species is closely allied to, and perhaps identical 

 with, the form described by Oeinitz i as Chonetes glabra; but this naine, however, 

 was preoccupied by Hall in 1857, for a species from the Upper Helderberg. 



PLEUROTOMARIA MODESTA. 



Shell small, sublenticular, spire greatly depressed, volutions six, obliquely flat- 

 tened above; body whorl very large, rapidly increasing in size, sharply angular on 



* Described and figured along with other forms in the Proceedings of the Academy 

 of Natural Sciences of Philadelphia, for 1888, pp. 232-246. 

 1 Carhonformation und Dyas in Nebraska, 1866, p. 60. 



