144 DISCOVERY REPORTS 



Dentition. Eales (1923) figured the radula of an example from McMurdo Sound in 20 m. and noted 

 that it showed characters intermediate between Buccinum and Cominella. 



The radula is decidedly more in accord with that of Cominella than with that of Buccinum, for it has 

 a tricuspid central and although the inner cusp of the laterals is incised to form several weak cusps 

 this tooth is still basically bicuspid. The boreal Buccinum on the other hand has six cusps on the central 

 and four on the laterals. The operculum also conforms more to that of Cominella than to that of 

 Buccinum. In Cominella and Neobuccinum the operculum has a terminal nucleus whereas in Buccinum 

 it is median submarginal with concentric growth lines. 



Genus Probuccinum Thiele, 191 2 

 Type (o.d.) : Neobuccinum tenerum Smith 



This is an Antarctic and Subantarctic Buccinuhim-like group characterized by a thin, semi-transparent 

 shell, ovate operculum with a small paucispiral terminal nucleus, and a radula with both the central 

 and lateral teeth tricuspid. 



The following species were ascribed to the genus by Thiele (19 12, loc. cit.) : Neobuccinum tenerum 

 Smith, 1907, Coulman Island, 100 fathoms; Probuccinum costatum Thiele, 1912, Gauss Station, Davis 

 Sea; Fusus (Neptunea) regulus Watson, 1882, Kerguelen I., 28 fathoms; Fusus (Neptunea) 

 edwardiensis Watson, 1882, between Marion I. and Prince Edward I., 140 fathoms; and Fusus 

 (Neptunea) scalaris Watson, 1882, north-west Patagonia, 125 fathoms. The latter, however, seems to be 

 a Pareuthria. 



Hedley (191 6) added a further species in Probuccinum tenuistriatum from the D'Urville Sea in 

 157 fathoms, and Tomlin (1948) recorded tenerum from 69 m. off Macquarie I. 



Probuccinum delicatulum n.sp., PI. VII, fig. 28 



Shell ovate-fusiform, truncated below, thin, semi-transparent, white, covered with a very thin pale 

 buff epidermis. Whorls six, including a large, smooth, dome-shaped protoconch of 2 \ whorls. Post- 

 nuclear sculpture of weak, very numerous, dense spiral striations crossed by crowded, somewhat 

 irregular, faint, crisp, axial growth lines. There are about thirty-two spirals on the antepenultimate 

 and about forty-five at the close of the penultimate whorl. The axial growth lines are nowhere strong 

 enough to assume the role of axial ribs, and a casual impression is that the shell is smooth. Spire about 

 one and an eighth times height of aperture, \perture obliquely D-shaped; outer lip thin, steeply 

 descending from the suture, effuse below the middle and flattened basally, with a broad, very shallow 

 anterior notch. In profile the outer lip is slightly insinuated just below the suture. Columella and 

 parietal wall with an evenly arcuate, narrow, thinly glazed callus. Operculum horny, ovate, with 

 a small, paucispiral, apical nucleus, Fig. N, 123. 



Height 20-5 mm.; diameter 10-5 mm. (holotype). 



Height 16-0 mm. ; diameter 8-o mm. (St. 160). 



Type locality. St. 140. Stromness Harbour to Larsen Point, South Georgia, from 54 02' S, 

 36 38' W to 54 11' 30" S, 36 29' W, 23 Dec. 1926, 122-136 m. 



St. 159. Off South Georgia, 53 52' 30" S, 36 08' W, 21 Jan. 1927, 160 m. 



St. 160. Between South Georgia and Shag Rocks, 53 43' 40" S, 40 57' W, 7 Feb. 1927, 177 m. 



Dentition. Fig. K, 63, p. 193 (holotype). Compared with Thiele 's figure of the radula of tenerum 

 (Fig. K, 64) the central tooth is proportionately wider, not sinused at the base, and the three cusps are 

 of equal size, not with the central one stronger. 



Operculum. Fig. N, 123, p. 196. 



