202 EMARGINULIN.SE. 



branches. The genera of Emarginulince exhibit nearly every stage 

 from a Patella-like shell to the centrally perforated type. The more 

 simple and primitive forms are Scutus and Subemarginula ; then 

 follow Emarginula, Rimula, Puncturella, and finally Glypliis, the 

 most modified form. 



The generic groups of this subfamily are moderately well-defined, 

 and our ideas respecting their affinities and systematic importance 

 will probably stand the test of time in essentially their present form. 

 The following analysis of genera is based on shell-characters for the 

 convenience of conchologists; but it should be remembered that a 

 study of the soft parts of most of the genera has fortified the posi- 

 tions taken. 



Key to Genera and Subgenera of Emarginulince. 



I. Apex in front of the middle, absorbed by the hole, the latter 

 bounded inside by a distinct oval hole-callus, truncated behind. 



Genus GLYPHIS Cpr. 



II. Apex central or post-median, persistent or absorbed ; anal fis- 

 sure either a closed hole or a slit open in front ; no distinct 

 hole-callus, but having a septum or " deck " extending forward 

 from back of the fissure, inside. 



A. Anal fissure a closed hole at summit or on the front slope, 



Genus PUNCTURELLA Lowe. 



a. Apex persistent, the fissure in front of it. 



1. Fissure at the summit, Section Puncturella s. s. 



2. Fissure on the front slope, Section Granopsis Ad. 



b. Apex absorbed by the oval fissure ; surface without radi- 

 ating riblets, Section Fissurisepta Seg. 



B. An open fissure in the front margin, Genus ZEIDORA Ad. 



III. No internal hole-callus or septum ; apex not absorbed. 



A. A siit-fasciole or band in front, distinctly differentiated 

 from the other radiating riblets, extending upward from 

 the fissure, Genus EMARGINULA Lam. 



a. Fissure an open anterior slit, Subgenus Emarginula s. s. 



b. Fissure a closed hole on the front slope, 



Subgenus Rimida Defr. 



B. No distinctly differentiated slit-fasciole or band ; ends of 

 muscle-scar distinctly hooked inward ; shell having radia- 

 ting ribs or riblets and crenulated edge, slit short or none 



Genus SUBEMARGINULA Blainv. 



C. No anterior slit or slit-fasciole ; muscle scar near the edge 



