166 SYSTEMATIC ARRANGEMENT 



central series 1 • 5 • 1 • 5 • 1 ; central small, laminal, narrow at top, wide 

 below ; inner lateral 4 • 4, linear, similar, subequal, oblique ; apex 

 rounded, slightly recurved ; central lateral very large, versatile, 

 capable of covering the inner lateral, conical, claw-like, transparent, 

 curved, acute at the tip, with a large notch at the inner side near tbe 

 base ; outer lateral very numerous, hair-like, transparent ; apex 

 bent, hooked (fig. 89). 



11. Clypidella. 



Mantle partly covered by the edge of the shell, double-edged ; 

 edges fringed and crenated ; anal siphon fringed, exposed ; foot 

 large, fleshy, with a few beads on the front part of the sides. Shell 

 ovate, shield-shaped, radiately rugose ; front edge sinuous, subtrun- 

 cated ; anal perforation elongate, subanterior. 



1 . C. pustula. 



12. Capiluna. 



Mantle partly reflexed on the edge of the shell, bearded on the 

 edge ; anal siphon projecting. Shell oblong, cancellated ; apex sub- 

 central ; anal perforation large, oblong ; aperture expanded, crenu- 

 lated on the edge ; inner edge of the anal perforation callous, and 

 rather produced behind. 



1. 0. Cuvieri, t. 110. f. 6. 



This genus differs from Lucapina in the shell not being perma- 

 nently covered by the mantle. 



fj-f Shell permanently covered by the mantle ; edge rounded, 

 crenated. 



13. Fisstjrellidaa. 



Mantle large, thickened on the edge ; foot very large, elongate. 

 Shell depressed, oval, slightly radiated ; anal perforation very large, 

 subcentral ; aperture open, with a smooth margin, thickened on the 

 inner edge. 



1. F. hiatula. 



2. F. megatrema, t. 112. f. 2. 



14. Lucapina. 



Mantle large, thin. Shell oblong, depressed, cancellated; apex 

 subcentral ; anal perforation large, simple ; aperture expanded ; edge 

 crenulated. 



1. L. cancellata. 



2. L. crenulata. 



