1922] NATURAL SCIENCES OF PHILADELPHIA. 37 



LL. A-central without well-developed cusps; with 

 heavy edge. 

 N. A-central with one or two points on heavy 

 cutting edge; comb-lateral with numerous 

 rounded cusps; C-central with two rounded 

 points and sometimes 1 or 2 smaller ones; 

 operculum as in Tristramia s. s., depressed, 

 angular, shells, usually with well-marked 



spiral striations Section Angulata. 



NN. A-central without cusps; comb-lateral 

 with broad, spatulate cusps; operculum 

 with calcareous plate thin, weak, and 

 usually incomplete; globose shells, usu- 

 ally with poorly marked spiral striations 

 O. 4 cusps on C-central .... Section Tenuis. 

 00. One rounded hook on C-central 



Section Tristramia. 



JJ. A-central Alcadia-like or highly modified; marginals 



with tendency to reduce number of cusps and 



to develop one or two primary ones, with others 



arranged along outer side; calcareous plate of 



operculum usually better developed than horny 



plate. 



P. A-central hood-shaped; comb-lateral with long 



and pointed cusps; accessory plate large but 



thin Lucidella. 



Q. A-central with well-developed cusps on margin; 

 C-central without lateral cusp; shell with lip 



entire, perforate Subgenus LindsleyaV. '. 



QQ. A-central without well-developed cusps on 

 margin; C-central with accessory cusp on 

 outside margin; shell imperforate; usually 

 toothed 

 R. C-central long and slender; few cusps on 

 comb-lateral (6) ; small species 



Subgenus Poenia. 

 RR. C-central broadly lanceolate ; many cusps 

 on comb-lateral (9-10); larger species 



Subgenus Lucidella. 

 PP. A-centrals not hood-shaped; comb-lateral with 

 spatulate or very few (3) cusps; accessory 

 plate smaller, but usually heavy. 

 S. Paired centrals Alcadia-like; comb-lateral 

 heavy with at least 6 cusps; inner mar- 

 ginals bicuspid Schasicheila. 



T. Only few (1-4) marginals bicuspid; shells 

 heavy, Analcadia-like; Western Cuba 



Subgenus Emoda. 



