330 THE VOYAGE OF H.M.S. CHALLENGER. 



This species conforms fairly to the type, Columbdla nana, Lov., for which Dr Gwyn Jeffreys 

 suggested the subgeneric name of Thcsbia (see Brit. Conch., vol. iv. p. 359). I have followed Pro- 

 fessor G. 0. Sars in connecting the group with the Plcurotoma family, but am unable to follow him 

 in giving it the dignity of a genus, nor can I, in the face of his type, accept " spira breviuscula" as 

 one of its characteristics (Moll. Axct. Norv., p. 221, see pi. xvi. fig. 2). 



60. Pleurotoma (Thcsbia) translucida, Watson (PI. XXV. fig. 11). 



Plcurotoma (Thesbia) translucida, "Watson, Prelim. Report, pt. 9, Journ. Linn. Soc. Lond., vol. xv. 



p. 444. 



Station 145. December 27, 1873. Lat. 46° 43' S., long. 38° 4' 30" E. Half-way 

 between Marion Island and Prince Edward Island. 140 fathoms. Volcanic sand. 



Station 149b. January 17, 1874. Lat. 49° 28' S., long. 70° 30' E. Entrance of 

 Royal Sound, Kerguelen. 25 fathoms. Volcanic mud. 



Station 149d. January 20, 1874. Lat. 49° 28' S., long. 70° 13' E. Royal Sound, 

 Kerguelen. 28 fathoms. Volcanic mud. 



Animal. — Foot fuscous olive, large, thick, square in front, pointed behind. Mantle 

 paler. Siphon rather short. Head and tentacles pale. Eyes large and black, on the 

 upper outer side and at about a fourth of the length of the tentacles, which are rather 

 solid, long, and cylindrical ; between these, and a little above them, is the large pro- 

 minent expanded snout, with a large circular opening in front, round which the edge of 

 the snout projects like a thick fleshy fringe. There are two unequal branchial plumes. 

 The radula consists of exceptionally minute, acicular, sharp-pointed, horny prickles. 

 There is no operculum. 



Shell. — Thin, horny, smooth, oval, with a tumid body-whorl, a rather high, subscalar, 

 small-pointed, round-whorled, shallow-sutured conical spire, and a tumid lop-sided base, 

 pointed at the pillar, but with scarcely any snout. Sculpture : Longitudinals — there are 

 close-set fine hair-like lines of growth ; under the microscope a system of much finer 

 regular striae is seen to cover the whole surface. Spirals — there are many fine, irregular, 

 and unequal rounded striae, which faintly appear on the surface, but are distinct on the 

 pillar and front of the shell : besides these, there are fine microscopic smooth scratches. 

 Colour white, with a faint tinge of yellow, horny, translucent, with a smooth and shining, 

 but hardly glossy surface. Spire rather high, conical, subscalar, from a slight bulge of 

 the shoulder. Apex : 2^ embryonic whorls, subcylindrically conical, rising to a small, 

 rounded, slightly immersed tip, which is a little bent down on one side. Whorls 6 in 

 all ; they are rounded, tumid, with a faint subangulation below the sinus-area, in which 

 there is a flattening rather than a constriction of the surface ; below the periphery of each 



