1896.] NATURAL SCIENCES OF PHILADELPHIA. 315 



CATALOGUE OF THE SPECIES OF CERION, WITH DESCRIPTIONS 



OF NEW FORMS. 



BY HENRY A. PILSBRY AND E. G. VANATTA. 



The genus Cerion, or as it is commonly known, Strop hia, is one of 

 the most characteristic forms of West Indian land-molluscan life. 

 With two exceptions the species are all insular ; C. incanum and C. 

 Antonii only, the former from South Florida Keys, the latter reported 

 to be from Guiana, are continental. The Greater Antilles — Cuba, 

 Hayti and Porto Rico, with the Virgin Is, and the entire group of 

 the Bahamas, are inhabited by numerous species, with a multitude 

 of local races. South of the larger islands named, if we include 

 with Cuba the faunally dependent Cayman group and Isle of Pines, 

 but one single species is found, C. uva of Curacoa, singularly isolated 

 in characters as well as geographically. Jamaica is without a 

 species; and the genus also fails in the Caribbean chain. 



In the main, each species is confined to some single island, or to a 

 series of adjacent keys or islets ; but there are numerous exceptions, 

 where forms unquestionably conspecific are found on several islands 

 separated by considerable distances. 



The species are subject to a remarkable range of individual and 

 local variation. Thus, many species vary from strongly and con- 

 spicuously ribbed to entirely ribless and smooth. In fact this is a 

 common variation, incontestably established by the series we have 

 examined of Cerion dimidiatum, C. columna, C. regina, C. uva, C. 

 maritimum, C. Sagraianum and many other species. Color is equally 

 variable, pure white species varying to heavily brown-mottled, and 

 this not in one, but in many of the species. Absolute size of adults 

 is almost as mutable as in Cijprcea; and occasional individuals are 

 abnormally shortened by the premature assumption of the features 

 of maturity, giving them a stunted appearance. 



All of these considerations render the study of the species one of 

 unusual difficulty ; and the older authors, unacquainied with the 

 protean nature of the species, as with the usually restricted range of 

 each, often failed to properly discriminate them. Thus, the several 

 volumes of Pfeiflfer's Monographia Heliceorum- Viventium are un- 



