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Show 1894.] MR. WALTER GARSTANG ON COLPODASPIS PUSILLA. 665 frequently 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 colour could be seen through the skin in the anterior part of the posterior prolongation of the mantle, where this organ lay beneath the foot. This glandular mass of an orange colour in all probability represents the " rounded brownish-yellow mass " observed by Sars in a similar position and termed by him the liver. The anterior edges of the foot, the dorsal and posterior edge 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 elevated 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 terminates in an obtusely rounded extremity. H e further states that its anterior edge is divided in tbe 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 interpretation must be made of the anterior parts of the foot. The two lappets, which in Sars's 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 .ZEolids, but differing from the latter in their greater size and obtuse extremities (PI. X L I V . fig. 2). Sars's 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 m y 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 a m strongly inclined to regard them as homologous Avith those pleuropodiall expansions so frequently met with among Opisthobranchiate mol-lusks. This view receives strong support from the fact that in Eaminea hydatis of the Mediterranean (which appears to be a different species from the H. hydatis of British naturalists) the pleuropodia, according to Boule2, are scarcely developed except on the sides of the anterior region of the body. Here-to judge from Boule's figure-they form elongated obtuse flattened expansions of the foot remarkably like those of Colpodaspis, differing only in their greater size and in their power of retroflexion over the back of the body. 1 The term pleuropodia was suggested by me in 1890 as a substitute for the undesirable word parapodia as applied to the lateral pedal expansions of Opis-thobranch mollusks, and has been accepted by Bergh and other writers (Journ. M . B. A. i. p. 419). 2 Roule, " Recherches sur les Tectibranches etc.," Ann. Mus. Hist. Nat. Marseille, 'ii. 1885, M e m . no. 3, p. 22, fig. 13. |