* 



36 PROCEEDINGS OF THE ACADEMY OF [Vol. LXXIV 



of cusps increasing rapidly towards outside; 



shell more globose Section Siiccincta. 



FF. A and B centrals with heavy knob-like cusp- 

 bearing backs; capituliform processes heavy 

 and interlocking; marginals ligulate; operculum 

 heavy and usually with inferior point, which 



fits into notch in lip Subgenus A Icadia. 



H. Smallish shells with notch in lip less well- 

 developed; comb-lateral with more pointed 



cusps Section Idesa. 



HH. Larger shells with well-developed notch or 

 lower lip of aperture; comb-lateral with 

 large spatulate cusps: R-central longer 



than broad Section A Icadia s. s. 



CC. Accessory plate smaller with reflection (slightly de- 

 veloped or absent) which at most only invests the 

 outer tip of the prolongation of the thickened upper 

 edge of the comb-lateral; centrals and opercula 

 various. 

 J. A-central with cusps like Oligyra, or with a thickened, 

 cuspless cutting edge; marginals with tendency 

 for the numerous cusps of each tip to arrange 

 themselves in a transverse row; operculum with 

 calcareous plate poorly-developed, often incom- 

 plete towards palatal margin; horny plate well- 

 developed and bright-colored, usually red 



Helicina. 

 K. Marginals sickle-shaped with well developed 

 lateral wings near tips; A-central with shelf-like 

 projection bearing the cusps; accessory plate 

 with small body but large lanceolate appendix, 

 and with the reflected anterior edge forming a 

 lather prominent shelf; operculum and comb- 

 laterals as in Tristramia. s. s 



Subgenus Helicina. s. s. 

 KK. Marginals quite strictly ligulate; A-central and 

 accessory plate not as preceding 



Subgenus Tristramia. 

 L. All paired centrals with well-developed cusps; 

 calcareous plate of operculum usually 

 somewhat thickened above nucleus, opaque 

 ii ii Iky -white to bluish; shells usually with 

 spiral s! riations 

 -M. Comb-lateral with numerous (9-11), long, 

 sharp cusps; shell depressed, angular to 



subangular Section Oxyrhombus. 



MM. Comb-lateral with more rounded cusps 

 (8 LO); shell globose. ...Section Tamsiana. 



