Mr. W. Clark on the Animals of the Bullidse. 105 



know he has taught us, and those who have gone beyond him in 

 the useful di-udgery of detail, must not forget that M. Cuvier, 

 like Newton and Columbus, pointed out the path, and taught 

 them the principia. 



Bulla cylindracea, auctorum. 

 Crjlichna cylindracea, Loven. 



Animal cylindrical, elongated, convolute; mantle not thick, 

 rarely produced beyond the front and lateral margins of the shell ; 

 it is edged with a series of minute red papillae ; the linear poste- 

 rior accessorial lobe of the foot lies within it, and resting on the 

 columella gives the mantle the appearance of being thickened ; 

 the surface of the shell in live and perfect specimens is covered 

 with an olivaceous or orange-brown epidermis. 



It is now necessary to make an extract from M. Loven's ge- 

 neric diagnosis : " Oculi sub eorum basi immersi ; solea brevis- 

 sima, ovato-quadrata ; pallium limbo incrassato aperturam pos- 

 tice claudens." If our views of the mantle and foot are correct, 

 it would appear that the linear posterior lobe of the foot has been 

 mistaken for a component part of the mantle, giving that organ 

 the crassitude mentioned by M. Loven. There are no eyes in 

 this species. M. Cuvier ascribes to the genus Bulla four ten- 

 taenia : what are called the superior pair, are, as we think, the 

 posterior lateral flaps of the head-disc, being the floating margins 

 of the solution of continuity of the disc from the neck ; the in- 

 ferior pair are the mere roundings of its anterior part, aided by 

 a narrow circumferential groove and a central indentation, that 

 give the aspect of ears; but neither pair have the similitude or 

 functions of the tentacula of the Pectinibranchiata. The flaps 

 occasioned by the deep sinus, at the under part of the foot, are 

 quite as produced as the superior pair of M. Cuvier, and may as 

 well be called tentacula ; it is surely a misnomer to call these 

 appendages by that term in any of the Bullida ; their only use 

 seems to be that of fins or paddles to assist in locomotion, either 

 by creeping or swimming. The head-disc is usually white or 

 pale yellow, of subquadrangular shape ; it I'ests 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 accessoi'ial 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 

 Ann. 6f Mag. N. Hist. Ser. 2. Vol. vi. 8 



