252 PATELLID^. 



Emarginula, Puncturella and Pileopsis, will form the group 

 which I term Cervicobranchiata, the branchial plumose appa- 

 ratus being single or double. 



In natural order, we consider that the first genera of this 

 family are Fissurella, Emarginula, Puncturella and Haliotis ; 

 which are well distinguished from the succeeding Patelloid 

 forms, by the double branchiae that descend symmetrically on 

 each side the neck ; and by the heart with its two auricles 

 embracing the rectum, which debouches wherever the fissure 

 or perforation in the shell is situate; these points, with 

 the symmetry of the testaceous cone in all, except Haliotis, 

 almost lead us to suppose that we have not yet done with 

 the Cbnchifera, and induce us, from the like parity of the 

 branchial organs, to place these genera next to the Chitons. 



* With double symmetrical branchial leaves, and the heart and two auricles 

 clasping the intestine. 



FISSURELLA, Bruguiere. 



F. RETICULATA, Donovan. 



F. reticulata, Brit. Moll. ii. p. 469, pi. 63. f. 4, 5; (animal) pl.B.B. f. 7. 

 Patella Grceca, Auctorum. 



Shell symmetrical, oblong, bluntly subconical, perforated at 

 the apex, and roughly reticulated. 



Animal at the base suboval, forming an obtuse pyramid, 

 having the mantle cloven at the summit to meet the perfora- 

 tion behind the vertex, which is anterior, but becomes merged 

 in the fissure of adult shells. The mantle is fleshy, and 

 thickened as it approaches the margins of the cone, and there 

 acquires a coriaceous texture, being produced into a tumid 

 rouleau, with a dentated or furbelowed frill, garnished with 

 stout papillae ; in adult animals the mantle can scarcely be 

 withdrawn within ; the outer surface is studded with minute 

 yellowish-white eminences, having between them light brown 

 lines or blotches ; the inner side is flake-white, mixed with 

 short lead- coloured lines. The head is a short muzzle issuing 

 from a small puckered extension of the mantle, marked at its 



