228 Lamarck's Genera of Shells. 



Shell solid, smooth ; of the same length as the back of the 

 animal ; margin ratlier thick. 



New Holland. PI. VII. Fig. 115. 4 Species. 

 2. Emarginula*. 



Body creeping. Two conical tentacula, with eyes at their 

 external base ; mantle very large, partly covering the shell with 

 its folds ; foot broad, and very thick. 



Shell scutiform, conical ; vertex inclined ; cavity simple ; 

 posterior margin notched, or emarginate. 



The shells of this genus are generally small; some of them 

 are considerably convex, in form of a cone, inclined towards 

 the anterior margin, which is always the narrowest, and oppo- 

 site to that which has the fissure. In others, the cone is very 

 much flattened, and scarcely perceptible. 



Type. Emarginulajissura't. (Patella fissura, im?i.) 



Shell oval, convex-conical, decussated with longitudinal ribs 

 and transverse stiire, pellucid, whitish ; vertex curved ; margin 

 crenate. 



European seas. PI. VII. Fig. 116. 2 recent species, and 



3 fossil. 



3. FissurellaJ. 



Head of the animal truncated anteriorly. Two conical tenta- 

 cula, with eyes at their external base ; mouth terminal, simple,- 

 without jaws. Two pectinate branchiae projecting from the 

 branchial cavity on each side of the neck ; mantle very ample, 

 projecting beyond the shell ; foot wide, very thick. 



Shell scutiform, or depressed conical ; concave on the under 

 side ; vertex perforated ; foramen oval, or oblong ; no spire. 



Some of the Fissurellce are of considerable size and thickness. 

 The hole on the summit is never round. 



Type. Fissurella nimbosa^. (Patella nimbosa, Lmw.) 



Shell ovate-oblong, convex, brownish white, with violet- 

 brown rays ; longitudinal striae numerous, crowded ; margin 

 crenate ; foramen oblong. 



• Derived, we suppose, from emarginatus, in allusion to the fissure in the 

 posterior mergin. 

 t Afissure. 



I Dim. fTomJismra,a little fissure. 

 § Cloudy, Lamarck's second species ; his type is F. picta. 



