138 GENUS XXXII. PATELLA. 



Adanson lias not altered tliis genus ; but Lamarck has di- 

 vided it into eight, as follow : 



Patella. Shell oval or shield-shaped, not spiral, concave, 

 without perforation or marginal fissure (see P. testudi- 

 naria, pi. 9. /. 126). 



FissuRELLA. Shell buckler- or shield-shaped, without a spire, 

 concave beneath, the vertex perforated with an ovate or 

 oblong opening (see P. grceca, pi. 9. /. 1 23). 



Fmahginula. Shell like a conical shield, the vertex inclined, 

 and the posterior margin slit or notched (see P. Fissura, 

 pi. 9. /. 127). 



Crepidula. Shell oval or oblong, convex above, with its apex 

 inclined to one end, and its cavity partially interrupted 

 by a horizontal division (see P.fornicata, pi. 9.f. 124). 



Concholepas. Shell oval, convex above, the apex obliquely 

 inclined to the left side ; the interior cavity simple ; with 

 two teeth, and a hollow at the base of the right edge (see 

 Favanne, t. 4. f 2; Chemn. 10, p. 320. vign. A.B.) 



Calyptrea. Shell somewhat conic, with the apex erect, en- 

 tire and pointed ; the cavity furnished with a convoluted 

 lip or little tongue like a horn, isolated or extending 

 from one side, like the blade of a knife running spirally 

 (see P. equestris, pi. 9. /. 122), 



AcARDO. Shell formed by two flattened and nearly equal valves, 

 having neither hinge nor cartilage, but a nmscular impres- 

 sion in the middle of the valves (see P. sinica Davila, pi. 2. 

 f. A.; and Chemn. 10. pi. 169. f. 1645-1646. 



