178 FISSITRELLIDIN.E. 



Subfamily II. Fissurellidin^:, Pilsbry. 



Animal much too large to be included in the shell, even when 

 contracted in spirit. Rhachidian tooth far broader than the laterals, 

 not narrowed above. Shell with the apex removed by a large per- 

 foration, which is bounded inside by an entire, not truncated, callus 

 rim. 



It is not improbable that Macroschisma and Lucapinella will be 

 found to belong elsewhere ; in this case, the subfamily will be re- 

 stricted to the forms included under my first division in the con- 

 spectus of genera. 



The shells of this group may generally be recognized by the large 

 perforation, gaping extremities, and entire, not truncated, hole- 

 callus. 



I have used shell-characters as largely as possible in the following 

 analytical table, which represents, however, the natural grouping of 

 the forms as I understand them. 



Conspectus of Genera. 

 I. Mantle wholly or in part covering the shell, and enveloping 

 the foot ; its border without papillae. 



A. Shell with a white rim or border above; very small in 

 proportion to the animal ; mantle extending far. beyond the 

 foot on all sides. 



a. Edge of shell rounded ; mantle-margin thickened. 



Genus Fissurellidea, Orb. 



b. Edge of shell grooved, acute ; mantle margin thin. 



Genus Pupilljea, Gray. 



B. Shell not white-bordered above, more than half the length 

 of the animal ; mantle extending but little beyond the 

 borders of the foot. 



a. Edges of shell nearly in a plane, finely crenulated, the 

 ends not elevated. Genus Lucapina, Gray. 



b. Edges of shell elevated at each end, blunt at the sides, in 

 adults not crenulated. Genus Megatebennus, Pils. 



II. Mantle not enveloping either shell or foot, the latter large and 

 fleshy, produced posteriorly beyond the shell ; shell with the 

 posterior margin more or less elevated, sides and front margin 

 in a plane. 



A. Apex of shell posterior, removed by a large triangular fis- 

 sure, the wide end of which is very near the posterior margin 



of shell ; tentacles long, subulate. 



Genus Macroschisma, Sw. 



