FOSSSAIIID.E. 235 



Subgenus SPIRONEMA, Meek, 1864. 



Shell ovate; whorls rounded, and separated by a rather deep 

 suture ; aperture ovate, lip thin, continuous ; columella not thick- 

 ened, perforated by a very small umbilicus ; surface with revolving 

 lines and furrows. L. TENUILINEATA, Meek and Hayden (Struct. 

 & Syst. Conch., t. 69, f. 35.) Cretaceous. Nebraska. 



FAMILY FOSSARID^. 



Head proboscidiform, with a median longitudinal sulcus; tenta- 

 cles thread-like, sharp, grooved ; eyes at their external base ; two 

 frontal lobes between the tentacles ; foot obtuse at both ends. 



Central tooth of the radula (PL 40, fig. 72) with a triangular, 

 finely dentate cusp ; lateral tooth transverse, with a strong cusp 

 and a series of fine denticulations its entire length ; marginals elon- 

 gated, simple. 



Shell turbinated, rather solid, white, grooved or ribbed spirally ; 

 aperture entire, lip simple, undulated, columella nearly straight. 

 Operculum corneous, subconcentric or subspiral. 



Genus FOSSAKUS, Phil., 1841. 



Shell perforate, subglobose, spirally ribbed, spire rather short, 

 last whorl large ; aperture semicircular, columellar margin nearly 

 straight, outer lip rounded, undulated. Operculum concentrically 

 grooved. 



The nucleus of the shell is .sharp, subcylindrical, of several 

 whorls, caducous. 



Animal having two frontal lobes. 



About fifty living species have been enumerated ; there are four 

 fossil species, miocene of Europe. F. AMBIGUUS, Linn. 



Maravignia, Aradas & Maggiore, 1841, is a synonym. 

 Section PHASIANEMA, S. Wood, 1842. 



No frontal lobes. ? Shell clathrate. F. SULCATUS, S. Wood, 

 Mediterranean and pliocene. 



Clathrella, Recluz, 1864, is a synonym. 



Section ISAPIS, H. & A. Adams, 1854. 



Shell umbilicated, spire elevated, cancellated, or with revolving 

 ribs; columella with a small median tooth, sometimes obsolete, 

 outer lip crenulated, interiorly grooved. West Indies, Mazatlan. 

 F. ANOMALA, Adams. 



