PATELLA. 261 
debarred access to marine vegetables ; their recorded descents 
from high levels, and periodical exits from, and returns to, 
the identical hollows they have made, after feeding on alge, 
have almost a fabulous complexion ; zones of sand fifty yards 
wide often intervene between them and such food, and their 
exceedingly slow locomotion is opposed to such manceuvres. 
As these animals are often for long periods prevented from 
obtaining animalcule from the water, it would appear that 
they have the power of drawing nourishment from the saline 
particles floating in the air, and extracted from their porous 
habitations. This idea is in some measure confirmed by the 
fact, that in all the animals I have observed of this species 
the intestine has always been filled with sand. I am now 
speaking of isolated individuals, which, however, are frequent 
and of all sizes. The great mass of the P.vulgata in the 
lower levels have the means of obtaimimg submersion and 
vegetable food. 
P. aTHLETICA, Bean. 
P. athletica, Brit. Moll. u. p. 425, pl. 61. f. 7, 8. 
The anatomy and external organs of this species scarcely 
differ from those of the P. pellucida, and as they have a still 
greater similarity to the P. vulgata, with which it has long 
been confounded, I will describe the principal variations, 
which, however, constitute sufficient specific distinction. The 
animal differs from P.vulgata in its much lighter colour, and 
in the substitution of the shades of orange-yellow for the lead- 
or pale smoke-brown. The mantle is edged with flake-white 
pointed filaments, twice as short and thick as in its congener. 
The branchial plates are longer, thinner, paler, and more arcu- 
ated at the terminations. The foot is of the various hues of 
orange-yellow, with scarcely any anastomosing lines. The 
head is of the palest purple; the tentacula pale yellow, shorter 
and more slender than in P. vulgata. Ido not, except m par- 
ticular cases, regard colour of much distinctive aid, but here 
the organic deviations corroborate this dubious character. 
This species has long been known on the Devon coast as 
the China Limpet, from the rich porcellanous interior aspect, 
