282 BULLID^E. 



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 in 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, 

 lying in the narrow aperture. 



This structure has given rise to M. Loven'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, sinuated in front. 

 These remarks, I think, explain, if I am not in error, M. 

 Loven'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 tentacida, 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 fsecal 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 



