COLPODASPIS. 29 



assumed in captivity in order to creep, after the manner of so many 

 Nudibranchs, along the surface-film, a large glandular mass of an 

 orange color could been seen through the skin in the anterior part 

 of the posterior prolongation of the mantle, where this organ lay be- 

 neath the foot. This glandular mass of an orange color in all prob- 

 ability represents the " rounded brownish-yellow mass " observed by 

 Sars in a similar position and termed by him the liver. The ante- 

 rior edges of the foot, the dorsal and posterior edges of the tentacles, 

 and parts of the ventro-lateral region of the mantle were ciliated. 



The animal consists of a foot, a small tentaculated head, an elev- 

 ated globose body, and a posterior tail-like pallial appendage. 



The Foot. Sars states that the foot is well developed and of 

 about the same length as the mantle ; that in front it is as broad as 

 the mantle, but becomes considerably narrower behind, and termin- 

 ates in an obtusely rounded extremity. He further states that its 

 anterior edge is divided in the middle by a deep incision into a pair 

 of lappets with rounded extremities. These statements are perfectly 

 borne out by his figures (pi. xi, figs. 1, 4); but comparison with 

 those supplied by myself shows that a somewhat different interpreta- 

 tion must be made of the anterior parts of the foot. The two lappets, 

 which in Sars' figures are shown to be directed forwards, are not 

 really, as he maintains, the divaricated halves of the anterior part 

 of the foot, but are rather to be regarded as a pair of expansions of 

 the antero-lateral margins of the foot, analogous to the anterior 

 horns of the foot in many Aeolids, but differing from the latter in 

 their greater size and obtuse extremities (PL 21, fig. 2). Sars' 

 figures also indicate that they are capable of being directed forwards ; 

 but I never observed them in this position myself, and must regard 

 the condition represented in my figures as more normal than the 

 former. These antero-lateral processes are so considerable that, in 

 view of the affinities indicated by other organs of Colpodaspis, I am 

 strongly inclined to regard them as homologous with those pleuro- 

 podial expansions so frequently met with among Opisthobranchiate 

 mollusks. This view receives strong support from the fact that in 

 Haminea hydatis of the Mediterranean (which appears to be a differ- 

 ent species from the hydatis of British naturalists) the pleuropodia, 

 according to Roule, are scarcely developed except on the sides of 

 the anterior region of the body. Here to judge from Roule's figure 

 they form elongated obtuse flattened expansions of the foot remark- 

 ably like those of Colpodaspis, differing only in their greater size 

 and in the power of retro-flexion over the back of the body. 



