SYSTEMATIC 121 



penultimate, forty-five moderately widely spaced on the body-whorl, plus a further twenty-five much 

 weaker spirals, which are crowded into the umbilical cavity. Spire about half height of aperture. 

 Umbilicus a narrow pit partially bridged by a thin-edged broadly reflexed columellar lip. Columella 

 vertical, basal section of lip rounded and thickened; outer lip thin. 



The differences between the several forms of sculpta are best shown in tabular form. (Spirals = 

 number of spiral grooves on the first post-nuclear whorl.) 



Height 9-0 mm. ; diam. 7 mm. ; aperture 7x4 mm. ; spirals [sculpta). 



Height 9-5 mm. ; diam. 8 mm. ; aperture 6-75 x 4-5 mm. ; spirals 16-18 (scotiatia). 



Height 9-0 mm. ; diam. 7-8 mm. ; aperture 6-5 x 4 mm. ; spirals 16-18 (scotiana). 



Height 8-9 mm. ; diam. 7-5 mm.; aperture 6-5 x 4 mm.; spirals 16-18 (scotiana). 



Height 8-5 mm. ; diam. 7-2 mm. ; aperture 6-o x 4 mm. ; spirals 16-18 (scotiana). 



Height 6-5 mm. ; diam. 5-0 mm. ; aperture 4-3 x 2-5 mm. ; spirals 12-17 (Form A). 



Height 6-3 mm. ; diam. 5-0 mm. ; aperture 4-5 x 2-5 mm. ; spirals 9-12 (Form B). 



Dentition. Fig. J, 50, p. 192. The radula is so minute that it must be almost functionless. The only 

 difference in detail between the radula of sculpta (Form, B, St. WS 773) and scotiana (St. 167) are that 

 the former has better developed cusps on the laterals and a bifid inner marginal. 



St. 45. 27 miles S 85 E of Jason Lt., South Georgia, 6 Apr. 1926, 238-270 m. 



St. 167. Off Signy I., South Orkneys, 6o° 50' 30" S, 46 15' 00" W, 20 Feb. 1927, 244-344 m. (holotype and 



numerous paratypes). 

 St. WS 32. Mouth of Drygalski Fjord, South Georgia, 21 Dec. 1926, 225 m. 



Genus Prolacuna Thiele, 1913. 



n.nom. for Sublacuna Thiele, 1912 non Pilsbry, 1895 



Type (o.d.): Sublacuna indecora Thiele ( = Frigidilacuna Tomlin, 1930, another 



substitute for Sublacuna Thiele, 19 12) 



Prolacuna indecora (Thiele) 



Sublacuna indecora Thiele, 1912, p. 195, pi. 12, fig. 4; pi. 15, fig. 19. 

 Sublacuna indecora Smith, 1915, p. 66. 

 Sublacuna indecora Eales, 1923, p. 21. 



Type locality. Gauss Station, Davis Sea. 

 St. 1660. Ross Sea, 74° 46-4' S, 178° 23-4' E, 27 Jan. 1936, 351 m. 



Range. Davis Sea to Ross Sea. 



Eales (loc. cit. pp. 21-3) figured the operculum, jaws and radula which, together with general 

 anatomical considerations, show that the genus is Naticoid. It differs from other Naticoids in two 

 unimportant details— the absence of a ' veil ' over the snout and the coalescence of the tentacle bases 

 in the mid-dorsal line. 



According to Thiele (191 2) the genus includes the following three species: Sublacuna trilirata 

 Thiele, 1912, Gauss Station; Lacuna macmurdensis Hedley (191 1) 10-20 fathoms, Cape Royds; and 

 Lacuna notorcadensis Melvill & Standen (1907), Scotia Bay, South Orkneys, 9-10 fathoms. 



It is doubtful if these heavily spirally keeled species are really congeneric with the smooth indecora. 



Prolacuna? macmurdensis (Hedley) 



Lacuna macmurdensis Hedley, 191 1, p. 4, pi. 1, fig- 6. 

 Type locality. 10-20 fathoms, Cape Royds, Ross Sea. 

 St. 1660. Ross Sea, 74 46-4' S, 178 23-4' E, 27 Jan. 1936, 351 m. 



