270 PLEUROBRANCHID. 
P. pLumuLA, Montagu. 
P. plumula, Brit. Moll. iti. p.559, pl. 114. F. £.6, 7; (animal) pl. X.X. f. 1. 
Animal throughout pale orange-yellow, except that on both 
surfaces its pellucidity causes the elongated oval, imcipient 
spiral, very patulous shield of the viscera to give the centres 
of both areas a dark lead appearance, in consequence of the 
purplish-ved colour of the shell. The mantle is oval, smuated 
at the margins, displaying throughout the upper surface an 
irregular network formed by fine whitish lines on the yellow 
ground-colour ; the meshes gradually progress from the centre 
of the apex to the marginal periphery ; the under surface is 
plain. The area of the mantellar disk considerably surpasses 
the pedal one. The foot is a smaller corresponding oval, 
also sinuated, rounded in front, and deeply emarginate be- 
hind at the anal pomt. The head at its junction with the 
body has a strong, flat, thick neck, which gradually extends 
into a compressed thinish apron, transverse, rounded in 
the centre, and forming at its right and left angles very 
short, blunt, imeipient tentacular flaps, as in some of the 
Bulle; the mouth is a transverse fissure beneath; the ten- 
tacula are large, approximate, thick ; apparently tubular, but 
are really membranes folded to simulate tubes, truncate at 
the extremities, with a muddy red-brown line in the centre 
from base to pomt; they spring from the neck at some little 
distance from its junction with the body, and bifurcate at an 
angle of about 45°. The eyes are large, black, immersed in 
the skin behind the bifurcation ; they are rarely seen, bemg 
carried on the march, which is much slower than in its con- 
gener, under the upper mantle. The animal, of which the 
above is an account, was sent to Bath, in sea-water, in De- 
cember 1850, and proved lively. 
To observe on the anatomy would be to repeat that of 
P. membranaceus ; its generalities are absolutely the same, 
with some scarcely appreciable specialties. Though the pro- 
gression of the animal is slow, it 1s in every respect superior 
to the Patelloid tribe, except Chiton, with which this genus has 
undoubted alliance. It is rare at Exmouth, but the acquisition 
