14 



FAMILY CYCLOSTREMATID&. 



Animal with ciliated, thread-like tentacles, the eyes on short pe- 

 duncles : snout bilobed ; foot elongated, truncate in front, and ex- 

 tending at each angle into a filament ; sides with three or four pairs 

 of ciliated cirri, and a pair of auricular appendages in front, be- 

 tween the cirri and the tentacles. Jaws scaly. 

 Dentition, 8'(4 + 1+ 4)'8, PL 1, fig. 4. 



Shell small, umbilicated, depressed, white, corneous or transpar- 

 ent, not nacreous ; aperture circular, with continuous, sharp peris- 

 tome. Operculum corneous, multispiral. 



Genus CYCLOSTREMA, Marryatt. 1818. 



Shell white, or uniformly colored, last whorl obliquely striate. 

 C. CANCELLATA, Marryatt. 



About 25 species have been described ; distribution nearly uni- 

 versal. Fossil, tertiary. 



Delphinoidea, Brown. 1727, is a synonym. 



Section CYCLOSTREMA (sensu stricto). 



Spire short, surface with spiral ridges, cancellated. 



Section TUBIOLA, A. Ad. 1864. 



Whorls rounded, simple, contiguous, spirally striate. C. SERPU- 

 LOIDES, Montagu. 



Section DARONIA, A. Adams. 1864. 



Planorbiform, spire depressed, concave, whorls rounded, more 

 or less disunited. C. SPIRULA, A. Ad. 



Subgenus THARSIS, Jeffreys. 1883. 



Globular, solid, polished ; aperture circular, peristome continuous, 

 adhering at the columellar margin; the umbilicus closed in the 

 adult by a callus. 



C. ROMETTENSIS, Seguenza. Atlantic, Mediterranean. 



Subgenus GANESA, Jeffreys. 1883. 



Naticiform, thin, always perforate, axis of the spire oblique; 

 aperture subcircular, peristome continuous. 



Atlantic Ocean; abyssal. C. PRUINOSA, Jeffreys. 



