270 PLEUROBRANCHID.E. 



P. PLUMULA, Montagu. 

 P.plumula, Brit. Moll. iii. p. 559, pi. 1 14. F. f. 6, 7 ; (animal) pi. X. X. f. 1 . 



Animal throughout pale orange-yellow, except that on both 

 surfaces its pellucidity causes the elongated oval, incipient 

 spiral, very patulous shield of the viscera to give the centres 

 of both areas a dark lead appearance, in consequence of the 

 purplish-red colour of the shell. The mantle is oval, sinuated 

 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 point. 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, incipient tentacular flaps, as in some of the 

 Bullce; 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 point ; 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, being 

 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 is 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 



