74 



THE NAUTILUS. 



with delicate narrow, separated ribs whicli break the continuity of 

 either margin and run obliquely to the median line where they form 

 a triangular space of ribs of unequal length, which do not reach the 

 lower margin ; the number of ribs on each side of the median line, 

 vary in the same species, as well as in the different species, the whole 

 number in each jaw varying from fifty-five to ninety-six ; the lingual 

 membrane is broad and the denticles vary in size in the different 

 species some being narrower than others. Shell dextral or sinistral, 

 varying from oblong ovate, to conic ovate, and from solid to thin 

 and translucent or hyaline. Labium often flat, and widely reflected, 

 occasionally revolute or concave, aperture ovate, or auriform, more 

 or less contracted by the wide and often dentate columella. Surface 

 with minute spiral strire w'hich are punctulate at the apex. 



This genus may conveniently be divided into two subgenera : 

 Partula (in the restricted sense) and Diplomorphi. The species of 

 true Partula I divide into two divisions and thirteen groups, each 

 of which is named for a characteristic species. 



I. Auriform Division. 

 1. Faba Group. 



P.faba Martyn. 

 P. citrina Pse. 

 P. vittata Pse. 

 P. radiata Pse. 



P. iiavigatoriaVfr. 

 P. planilabra Pse. 

 P.fusca Pse. 



p. faba. 



P. auriculata. 



2. Auriculata Group. 



P. auriculata Brod. 

 P. compada Pse. 

 P. thala Garrett. 

 P. hilineata Pease. 



3. Dentifera Group. 

 P. dentifera Pfr. 



P. formosa Pse. 



P. calif era Pfr. 



P. imperforata Pse., MS. 



P. virginea Pse., MS. 



p. dentifera. 



