GASTEROPODS. 173 



Muscular Scars. The internal scars so prominent in the 

 shells of living Capulus and modern allied genera are seldom 

 observable in Paleozoic forms. Hence, having never noticed 

 in individuals of the latter the peculiar horseshoe-shaped im- 

 pressions, Hall assigns this as the only reason for regarding 

 Capulus and Platyceras as distinct genera. Since the time that 

 the American author first expressed this opinion, a sufficient 

 number of fossil examples have been found to indicate clearly 

 the real nature of these scars. A careful comparison shows 

 that they are not very different from those of typical Capuli, 

 though considerable variation is noticeable in the several 

 forms, and even in shells of the same species. 



As exhibited in I.pabulocrinus, and some other species, the 

 muscular scars are connected by a narrow band traversing the 

 posterior side of the shell. In adult examples, the scars are situ- 

 ated about one-fourth the distance from the apertural margin 

 to the apex. In some excellent internal casts of Capulus pro- 

 tei (CEhlert) from the lower Devonian of Mayenne, the muscular 

 impressions are somewhat different from those of congeneric 

 species from America. The scar on the right side is compara- 

 tively large, oval and well defined ; a narrow sinuous baud passes 

 around the spire posteriorly and terminates on the left side in 

 an enlarged scar similar to but much smaller than that on the 

 right. In some specimens the linear band does not appear to 

 be perfectly continuous from one side to the other. 



Capulus subsinuosus (WORTHEN) 



Platyceras subundatum Meek & Worthen, 1868 : Geol. Sur. Illinois, vol. 



Ill, p. 387, pi. vii, figs. 13a-b and 14a-b. (Not Conrad, 1841.) 

 Platycwas subsinuosum Worthen, 1882: Illinois St. Mus. Nat. Hist., Bui. 2, 



p. 38. 



Shell composed of about three and one-half rounded volu- 

 tions, the first two and a-half or three of which increase rather 

 rapidly in size, are closely coiled together, and depressed with 

 the spire on a level with or below the upper side of the outer 

 turn ; body portion very rapidly expanding, so as to cause the 

 upper side to rise considerably above the inner turns, with 

 which, however, it continues very nearly or quite in contact, 



