664 ME. WALTER GAKSTANG ON COLPODASPIS PUSILLA. [Nov. 20, 



Fig. 4. Aulolcpis 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., branchio- 



stegal rays ; i.op., interoperculum ; op., operculum ; s.op., suboper- 

 culum ; other letters as above. [49903.] 



6. Ditto ; pectoral and pelvic arches, cl., clavicle ; ph., 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. 

 By Walter Garstang, M.A., F.Z.S., Fellow and Lecturer 

 of Lincoln College, Oxford. 



[Received November 20, 1894.] 

 (Plate XLIV.) 



The mollusk which forms the subject of the present communi- 

 cation 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 ; bat the few points in 

 which I have to modify, or supplement, Sars's interpretations seem 

 to render the position and relations of the genus somewhat 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 

 memoir * 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 was obtained a little later by Gr. 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 

 found 2 a specimen in the results of a day's dredging in the imme- 

 diate 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 which were associated Scrtidaria argentea, JJenricia (Cribella) 

 sanguinolenta, and a sponge resembling Bowerbank's figure of 

 Isodictya dissimilis (Brit. Spong. iii. pi. lv.). 



This Plymouth individual was one eighth of an inch (3*125 mm.) 

 in length. In colour it was snow-white, speckled with opaque 

 white spots. When the animal was inverted, a position which it 



1 M. Sars, Bidrag til Kundskab om Chri.stianiafjordens 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. 



