282 BULLID. 
locomotion, either by creeping or swimming. The head-disc 
is usually white or pale yellow, of subquadrangular shape ; it 
rests on and covers the foot, which is of similar form, and the 
central sinuations of the two coalesce. The foot, as in the 
type, extends from beyond the shell im front to its posterior 
extremity. At half its length from the front the continuity 
is interrupted by a deep hiatus, but at a lower level the linear 
or accessorial lobe progresses to the termination of the shell, 
lyimg in the narrow aperture. 
This structure has given rise to M. Lovén’s term “solea 
brevissima :’”’ he has only described the anterior or active part 
of the foot, or one-half of it, overlooking the posterior linear 
portion ; its apparent separation certainly puts on the appear- 
ance of a short distinct subangular foot, simuated in front. 
These remarks, I think, explain, if I am not in error, M. 
Lovén’s mistake relative to the foot and tumidity of the 
mantle. The division of the foot by the deep groove is 
doubtless, as in B. hydatis, to increase flexibility, and its 
under marginal flaps, with the upper ones of the head, mis- 
called tentacula, are probably to assist both pedal and nata- 
tory locomotion. The progression of the present animal, 
though otherwise it is sufficiently lively, often turning from 
one side to the other, is very slow. The sole of the foot is 
pale yellow or white, and is often well reflexed on itself at 
the sides, and sometimes up to the upper disc. The mouth 
is between the lobes; the fissure is vertical, and furnished 
with a buccal mass supported by corneous plates and a short 
spinous tongue. The stomach, as in the typical species, con- 
tains a gizzard composed of three minute, elongated, very 
black, rather pointed plates, flat within, convex without, and 
all of similar form. The branchial apparatus is a plume of 
short coarse strands lying in a crypt across the neck. The 
anus appears to terminate posteriorly, as that portion of the 
shell is always incrusted with sand, mucus, and fecal matters. 
The general aspect of the animal varies from pure white to 
pale orange-yellow, with occasionally a tinge of green. 
It inhabits the coralline and laminarian zones. 
This animal has the same leaflets at the sides of the buccal 
