14 CLASS Ill. GASTEROPODA. ORDER II. CYCLOBRANCHIATA. 
PATELLA, Auctorum. 
Testa elliptica, univalvis, non spiralis, patelleformis aut clypeiformis, 
depresso-conica, subtis concava; margine basali szpé crenato ; 
vertice plerumque subcentrali, anticé recurvo. Impressio muscu- 
laris elliptica, anticé interrupta. 
The title of Lepas, which is now used in reference to the preceding 
sub-kingdom of Invertebrata, appears to have been originally appro- 
priated to the animals vulgarly called Limpets. Whether the ancient 
Greeks derived this appellation from the word Xerac, a rock, as express- 
ive of their living attached to rocks, or from demic, a scale, or the rind of 
anything, in allusion to the manner in which the rocks become coated 
with them, it is unimportant to determine. The Latins distinguished 
the Limpets by the appropriate title of Patella, the name of a small 
deep dish used for carrying meat in their sacrifices; hence it is that, 
in the works of the early naturalists, we find the two names Patella and 
Lepas recorded as synonyms. The genus Patella was thus adopted by 
Linneus to include all mollusks having a patelleform or dish-shaped 
shell; and as the variations in their organization and habits have subse- 
quently become known, it has been distributed into the following genera : 
Fissurella, Emarginula, Calyptrea, Crepidula, Pileopsis, Hipponyx, Par- 
mophorus, Umbrella, Siphonaria, Lottia, Ancylus and Navicella ; and even 
these again have been still further subdivided by some authors. 
The shell of Patella may be described as being elliptic, univalve, not 
spiral, basin- or dish-shaped, of the form of a shield or depressed cone, 
and always concave beneath; the basal margin is often crenated all 
round ; the vertex or summit of the shell is mostly situated near the 
centre, and always recurved anteriorly, that is, towards the head of the 
animal. The muscular impression in the interior is elliptic, and inter- 
rupted in the same direction. 
