252 PATELLIDZ. 
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 Mssurella, Emarginula, Puncturella and Haliotis ; 
which are well distinguished from the succeeding Patelloid 
forms, by the double branchiz 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 im all, except Haliotis, 
almost lead us to suppose that we have not yet done with 
the Conchifera, 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, Brugwiere. 
F. reticuntata, Donovan. 
F. reticulata, Brit. Moll. u. p. 469, pl.63. f. 4, 5; (animal) pl. B.B. f. 7. 
Patella Greca, Auctorum. 
Shell symmetrical, oblong, bluntly subconical, perforated at 
the apex, and roughly reticulated. 
Animal at the base suboval, forming an obtuse pyramid, 
haying the mantle cloven at the summit to meet the perfora- 
tion behind the vertex, which is anterior, but becomes merged 
im 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 mto a tumid 
rouleau, with a dentated or furbelowed frill, garnished with 
stout papille; im adult animals the mantle can scarcely be 
withdrawn within ; the outer surface is studded with minute 
yellowish-white eminences, having between them lght brown 
lines or blotches; the imner 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 
