GASTROPODA. 1( "' :! 



Cjrrlon>4 llmatmii 1 



X.MA (?HoMPBA) UMATUM, fl. tp. (Ulrifh.) 



i-i. A 1 1 i \\\u. rios. 



1 15 to SO mm. In hlfht, the greatest width generally about a Jlfth lew, consisting, without th 

 us which Is unknown, of aUmt fmir rapidly enlarging ventrleone whorls; suture distinctly ImprMMd 

 though not deeper than nfcwwltated by the uniform conveilty of the whorls; aperture large, higher than 

 wide, rounded below, somewhat acumlnat* orate In outline; Inner Up nearly straight, not as thick as 

 usual In Cyelontma, while as a rule It Is merely flattened Instead of excavated, and turned Inward so that 

 th.- tut p"rtl"ti i* not fully visible In a ventral view; surface smooth, sometimes polUhed, the lines of 

 growth obscure: of revolving lines not a trace Is to be aeen except on two specimens where the surface Is 

 glossy M though they retained patches of epidermis that Is generally not preserved. 



In Its general aspect this One specie* reminds one strongly of Hoiopea, and It Is possible that It would 

 be more naturally placed In that genus. It has seemed to us, hom-vcr, that the characters of the Inner 

 Up, which it sometimes excavated as In Cyclonema, would not permit Its reference to Holopta, In which, 

 as the genus Is now understood, the Inner Up Is thin and simple. Perhaps C. fimadtm Indicates a partial 

 reversion to ancestral characters In other words, a form In which larval characters are retained through 

 adult stages. 



Jbrmotfoft and locality. Lower division of the Lorraine group, Cincinnati, Ohio. 

 CWtation.-E. O. Ulrlch. 



Genus STROPHOSTYLUS, Hall. 

 SrrofAostyiiu, HALL, 1859, Pal. N. Y., vol. Ill, p. 303 



Shell turbinate to subglobose, consisting of three to six rounded and more or 

 less ventricose whorls, with the spire elevated or low and the body whorl often very 

 large; mouth rounded, outer lip thin, sharp, columellar lip not very thick, very little 

 reflected, generally twisted and spirally grooved within; surface finely cancellated, 

 with either the revolving or the oblique growth lines the stronger. Type, S. eltgans 

 Hall. 



The earlier Lower Silurian species of this generic type have all comparatively 

 slender whorls, and forms of the same kind continue on at least to the close of the 

 Upper Silurian. These slender-whorled forms may at first sight look very different 

 from those rapidly expanding subglobose species for whose reception Hall proposed 

 the genus. But, that the latter were evolved from the former is, we think, 

 sufficiently indicated by the range of variation occurring in a single species like S. 

 cyclostomus Hall, of the Niagara. Specimens of this species before us approach our 

 widest ,S. Ifitilis very closely. As a rule the spiral element of the surface sculpture 

 is the stronger in the slender-whorled forms, while the lines of growth predominate 

 in the broader types. 



Comparing the genus with Cyclonema we find that the inner lip is thinner and 

 the fold on it more twisted, the whorls are more rounded and generaHy coiled with 

 lew constancy, most of the species exhibiting greater variation in the bight of the 

 spire than occurs in Cyclonema. Bat, as we have already stated under Cyclonntia, our 



