162 PROCEEDINGS OF THE ACADEMY OF [1890. 



Capulus infundibuhim (Meek & Worthen). 

 sulaatinus (Keyes). 



St. Louis Limestone. 

 Capulus acutirostris Hall. 



Kaskaskia Limestone. 

 Capulus chesterensis (Meek and Worthen). 

 ovalis (Stevens). 



Upper Carbonic. 



Lower Coal Measures. 

 Capulus sjyinigei'us (Worthen). 



Upper Coal Measures. 

 Capulus jKirvtisSwaWow. 



III. Descriptions of Species. 



Generic Diagnosis. Shell depressed, subglobose, or obliquely sub- 

 conic ; body whorl very large. Aperture ample, expanded ; labrum 

 more or less sinuous, inner lip not aiichylosed to the spire. Surface 

 ■glabrate, plicate or sometimes spiniferous ; lines of growth often 

 unibricate. 



The shells which have been referred to Platyceras present a man- 

 ifold variety of forms. It is, therefore, not improbable that a fuller 

 Bxamiuation and comparison of all the known species will demand 

 a somewhat diiferent arrangement and subdivision of the group than 

 that now existing. In this .section the shell presents few salient 

 characters for consideration. As already stated it is often with ex- 

 treme difficulty that the forms of this group can be satisfactorily 

 separated from certain varieties of Platystoma and various genera of 

 Patelloid shells. In general, however, the test of Cajmlus is coiled, 

 subspiral, arcuate or subconic with a relatively small spire and an 

 immense, rapidly expanding body whorl, while the surface is usually 

 without ornamentation. The large majority of the species of this 

 group possesses tough, massive shells which are generally, therefore, 

 in a much better state of preservation than most of the associated 

 molluscan remains. 



3fuscular Scars. The internal scars so prominent in the shells of 

 living Cajndus and modern allied genera are seldom observable in 

 paleozoic forms. Hence, having never noticed in individuals of the 

 latter the peculiar horse-shoe shaped impressions, Hall ^ assigns this 



1 12th Ann. Reg. Rep. 1859, p. 16. 



