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Show 1894.] MR. WALTER GARSTANG ON COLPODASPIS PUSILLA. 667 prolongations, " which can be mistaken for the posterior border of the foot when the animal is contracted." His figures unfortunately do not show this point at all well (pi. i. fig. 25), and Forbes and Hanley's figure, though clearer, does not seem to represent the anatomical relations correctly (I. c. pi. U U . fig. 4). In Philine aperta the plantar surface also consists both of foot and mantle; but this part of the mantle does not correspond with the pallial appendage of Colpodaspis, as it contains the viscera and shell. If it be examined, however, from the ventral aspect, tbe pallial siphon is seen on the left hand, as in Colpodaspis (fig. 2), and, to the right of the siphon, the mantle is seen to be prolonged into a short free membranous border, which overhangs the siphonal groove and even extends slightly behind it. The relations of this slight expansion are such that I think it may be regarded as the rudimentary, or probably vestigial, representative of the pallial appendage of Colpodaspis. Baclula.-This organ was not described in Sars's original paper, but a figure of it was given (AA'ithout description) in a later work by G. O. Sarsl. There is a single admedian series of sickle-shaped denticles on either side, and two series of slender laterals, the formula thus being 2, 1, 0, 1, 2. I was unable to lay open the contracted radula of m y specimen, owing to its excessive minuteness ; but I determined that the number of TOAVS in the radula was from 25 to 30, and isolated individual denticles and half-rows by teasing with needles. Some of these are drawn as figure 3 of m y Plate. The admedian denticles of this radula differ from those figured by Sars in presenting a sharp distinction between their terminal and proximal parts. The handle of the sickle shows an angular projection from its inner or concave edge, like the corresponding denticle in Cohbocephalus costellatus as figured on the same plate (fig. 16). The lateral denticles also furnish an additional point of resemblance between the radula? of these two types in that their points are slightly bent in a plane at right angles to that of their general surface, so that, Avhen the denticles are mounted flat upon a slide, their points are directed upwards towards the observer. Shell.-Sars has described the shell so accurately that I have nothing to add to his description; but m y figures, being on a larger scale, represent its form and Avonderful delicacy rather better. Summary.-On the whole, I think this Plymouth specimen presents features which indicate a slight advance on the organization of those described and figured by Sars. I may mention its greater size (3-125 m m . as compared with 2*5 m m . ) , the greater differentiation of the tentacles, pallial siphon, and admedian denticles, and perhaps some increased extension of the free margin of the shell. Affinities.-Sars was not quite certain whether Colpodaspis belonged to the Opisthobranchia at all, and was much impressed by the fact that the foot is attached to the body by a somewhat 1 ' Bidrag til Kundskaben o m Norges Arktiske Fauna. I. Mollusca Regionis Arcticje Norvegi£e ' (Christiania, 1878), plate xii. (Tabulae anatomic^) fig. 15. |
