142 FISSUEELLA. 



by a callus rim the outlines of which are entire, not truncated 

 posteriorly. 



The summit of the shell is always a little in front of the middle, 

 even in those forms having it subcentral, and the border of the shell 

 is in a plane, not elevated at the ends, except in the subgenus 

 Clypidella. 



The anatomical characters as far as known do not indicate more 

 than one genus in this subfamily. 



Genus FISSURELLA Bruguiere, 1791. 



Fissurella Brug., Encycl. Meth., Lamarck, An. s. Vert., and of 

 authors. 



Fissurella of early authors comprised all of the perforated limpets. 

 It is, of course, as now understood, much more restricted by the elim- 

 ination of the large-fissured forms (Fissurellidea etc.), and the genus 

 Glyphis, which belongs to the subfamily Fmarginulince. 



Details of the anatomy are given under the several subgeneric 

 heads. 



Sy?iopsis of Subgenera and Sections. 



I. Summit of shell near the middle ; basal margins level, not ele- 

 vated at the ends. Subgenus Fissurella Brug. 



a. Margin of shell not crenulated, dark-bordered inside. 



Section Fissurella s. s. 



b. Margin of shell crenulated, without a dark border. 



Section Cremides Ads. 



II. Summit leaning forward over the front end of shell ; basal 



margins level. Subgenus Fissuridea Sw. 



III. Shell flattened, shield-shaped, the two ends elevated, gaping ; 



perforation narrow, situated in front of the middle. 



Subgenus Clypidella Sw. 



Subgenus Fissurella. 



The anatomy of the typical species (F. picta and its allies) is not 

 thoroughly known. It appears that the mantle-edge is thick, cren- 

 ulated above and below, granulate or papillose on its rather broad 

 surface, the anal pore is surrounded by slender processes or papilla?, 

 and the row of epipodial papillse is continuous. In all of the species 

 of the genus, the mantle and animal are contained completely within 

 the cavity of the shell, in alcoholic specimens. 



