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Show 666 MR. WALTER GARSTANG ON COLPODASPIS PUSILLA. [Nov. 20, The foot, upon this interpretation, must accordingly be described as T-square shaped, with gracefully arched anterior wings and rounded extremities, and of about the same length as the shell-bearing portion of the mantle. The median furrow of its plantar surface is shown in m y drawing (fig. 2) to have the same extent as in Sars's specimens. The Head.-The grooved tentacles in m y specimen correspond with Sars's description, except that no mention is made in the latter of a low curved ridge which can be seen in my figure 1 crossing the anterior part of the head from side to side and connecting the postero-dorsal edges of the two tentacles with one another. The eyes also are much closer together in the Plymouth individual than they are represented to be in Sars's figures; and the statement of the latter that they are situated " close behind and within the base of the tentacles " cannot be said to be applicable in the present case. I do not, however, think that any great importance should be attached to these slight discrepancies. W h e n Colpodaspis pusilla is creeping upon a flat surface, the antero-lateral horns of the foot are just perceptibly in advance of the tentacles (fig. 1); but when the creature is swimming inverted at the surface of the water the tentacles w e then seen to be considerably in front of the horns of the foot (fig. 2). The Body.-I have no addition to make to Sars's account of the body proper, except that in the Plymouth specimen the edges of the pallial siphon were more closely apposed than seems to have been the case with Sars's individuals. Pallial appendage.-When the animal is creeping upon the bottom of a vessel, a broad flattened tail-like appendage projects behind the mantle and seems at first sight to be the posterior section of the foot. Examination of the animal from the ventral aspect, however, reveals that this appendage is in reality a posterior prolongation of the hinder margin of the mantle to the morphological left of the pallial siphon (fig. 2). Sars adduces no homologue of this peculiar appendage, but it is, in m y opinion, to be directly compared with the posterior pallial lobes of various genera of Bulloid Tectibranchs. For example, in Haminea cornea Boulex writes as folloAvs :-".. a sa partie pos-terieure le manteau devient assez chamu et fonne alors une expansion arrondie que de prime abord on serait tente de considerer comme Vextremite du pied. Cette expansion nous parait Ure Vanalogue du lobe pcdleal posterieur de droite que I'on observe chez le Doridium meckelii, metis qui serait prive de son flagellum." Forbes and Hanley2 mistook this pallial lobe for a " supra-caudal (equivalent to opercular) lobe," but they correctly describe it in Haminea hydatis as being " large and reflected on the spire." In Philine catena also, according to Boule3, the mantle terminates posteriorly in a convex margin, a little below which are twro fleshy 1 L. c. p. 19. 2 «British Mollusca,' vol. iii. p. 542, pi. U U . fig. 3, 3 I. c. p. 36. |
