OCR Text |
Show 664 MR. W A L T E R GARSTANG O N COLPODASPIS PUSILLA. [Nov. 2 0, Fig.4. Aulolepis typus; head, right lateral aspect, p., palatine process of maxilla; other letters as above. [P. 4247.] 5. Ditto; head, left lateral aspect, with gular plate (gu.). br., branchiostegal rays; i.op., interoperculum; op., operculum; s.op., suboperculum ; other letters as above. [49903.] 6. Ditto; pectoral and pelvic arches, cl., clavicle; plv., imperfect pelvic bone with fin ; s.cl., supraclavicle; sc, scapula. [47932.] All the specimens were obtained from the English Chalk, and unless otherwise stated the figures are of the natural size. Except the original of PI. XLIII. fig. 1, the specimens are preserved in the British Museum, and the numbers placed in brackets refer to the Register of the Geological Department. 2. On the Gastropod Colpodaspis pusilla of Michael Sars. B y W A L T E R G A R S T A N G , M.A., F.Z.S., Fellow and Lecturer of Lincoln College, Oxford. [Received November 20, 1894.] (Plate XLIV.) The mollusk AA'hich forms the subject of the present communication has been so rarely seen, and presents such interesting peculiarities, that no apology is needed for the description of a new specimen. In the main my observations confirm those of the discoverer of Colpodaspis, Michael Sars; but the few points in which I have to modify, or supplement, Sars's interpretations seem to render the position and relations of the genus someAvhat clearer than has hitherto been the case. The literature on Colpodaspis pusilla is not extensive, as the only original observations on the creature are contained in Sars's memoirl on the fauna of the Christiania fjord. Two specimens were found by Michael Sars at Drobak, one in August 1864 at a depth of 70-80 fms., the other in June 1865 at a depth of 20 fms. A slightly larger specimen wTas obtained a little later by G. O. Sars at Horten in 14-20 fms. Since the capture of these Norwegian specimens thirty years ago no additional individuals appear to have been obtained until on Feb. 21st of the present year (1894) I found2 a specimen iu the results of a day's dredging in the immediate neighbourhood of Plymouth, about two miles south of the Mewstone, at a depth of some 15 fms. The ground was rough, and consisted of hard clean red sandstone covered with Caryophyllia, with Avhich were associated Sertulana argentea, Henricia (Cribella) sanguinolenta, and a sponge resembling Bowerbank's figure of Isodictya dissimilis (Brit. Spong. iii. pi. Iv.). This Plymouth individual was one eighth of an inch (3*125 mm.) in length. In colour it was snow-Avhite, speckled Avith opaque white spots. W h e n the animal Avas inverted, a position Avhich it 1 M. Sars, Bidrag til Kundskab om Christianiafjordens Fauna, ii. (Christiania, 1870), pp. 70-74, plate xi. figs. 1-6. 2 Garstang, " Faunistic Notes at Plymouth during 1893-94," Journal Mar. Biol. Assoc, iii. 1894, p. 219. |