OF CONCHOLOGY. H 



Family CYCLOPHORIDiE. 



Shell conical, elongate or depressed, varying greatly in the 

 convexity of the whorls, as well as in solidity. Furnished with 

 an operculum, the various methods of the accretion of which 

 afford good generic characters. 



Animal famished with two tentacles, which are contractile 

 but not retractile, with eyes at their external bases. Unisexual. 



Remarks. — This family contains but one positively indigenous 

 representative in the United States, although very numerous in 

 species in the neighboring West Indian Islands. The presence 

 of the operculum distinguishes the shell, as the contractile, non- 

 retractile tentacles, with eyes at their external bases, do the 

 animal from all preceding families. 



Genus CHONDROPOMA. 

 1. Chondropoma dentatum, Say. 



Plate 18, figures 14—16. 



Conic, with 7 convex whorls, but generally truncate by the 

 loss of three whirls ; surface finely cancellated ; suture deep and 

 crenulated ; aperture broadly ovate, a little angular above, lip 

 continuous, slightly reflected ; umbilicus small. Yellowish or 

 brownish, with chestnut bands, sometimes interrupted so as to 

 form longitudinal squares or stripes. 



Length 12, diam. 4 mill. 



Key West, Florida. 



One of the figures represents this species suspended by a mu- 

 cous thread, which it can spin at pleasure. It possesses this 

 faculty in common with the naked slugs. 



Family HELICINID^E. 



Shell solid, depressed or lenticular, the whorls flattened, peri- 

 phery frequently angulated ; mouth half rounded, lip thick, 

 generally reflected ; umbilicus covered by a heavy deposit of 

 callus. Operculum heavy, its growth annular. 



