126 



D.G. REID AND C. OSORIO 



authors have distinguished a relatively smooth, northern species or 

 subspecies A. m. unicornis (Bruguiere, 1789) (= A. crassilabrum) 

 from the typical southern A. m. monodon with scaly spiral cords, 

 thinner shell and wider aperture (Dell, 1971; Wu, 1985; Vermeij, 

 1993). The two forms are said to overlap between 40 and 44°S and 

 have been recorded sympatrically (Dell, 1971; Wu, 1985), although 

 characters evidently intergrade in this region (Cernohorsky, 1977; 

 Wu, 1985). The present samples extend the geographical range of 

 this overlap; both shape and sculpture vary such that no clear 

 distinction can usefully be made on the basis of these characters, 

 and the two forms are provisionally regarded as conspecific until 

 more evidence becomes available. As in the similar ocenebrine 

 muricid Nucella (e.g. Palmer, 1990), shell form might be a func- 

 tional phenotypic response to the presence of crab predators, from 

 which the snails are at greater risk on shores protected from wave 

 action. Possible correlation of shell form with abundance of preda- 

 tory crabs on local and geographical scales has not been 

 investigated in A. monodon. However, it is notable that several 

 intertidal Littorina species in the northern Atlantic show analogous 

 variation in shell characters over a geographical scale, with thin- 

 shelled forms present only at high latitudes where predatory crabs 

 are rare or absent, producing a stepped cline (Reid, 1996). 



Trophon plicatus (Lightfoot, 1786) 

 (Figure 3N) 



Trophon laciniatus (Martyn, 1784) - Strebel, 1904: 199-203, pi. 3, 



figs 1-8 (non-binominal and therefore unavailable name). 

 Trophon (Stramonitrophon) laciniatus (Martyn, 1784) - Powell, 



1951: 156. 

 Murex plicatus Lightfoot, 1786: 104. 

 Trophon plicatus - Cernohorsky, 1977: 117, fig. 18. 

 Trophon (Stramonitrophon) plicatus - Castellanos & Landoni, 1 993 : 



5, pi. 1, figs 16-22. 

 Trophon (Stramonitrophon) lamellosa (Gmelin, 1791) -Dell, 1971: 



212 (synonymy). 



Description. Shell to 54 mm; fusiform with rounded whorls; 

 sculptured by prominent, lamellose varices (10-15 on last whorl), 

 each produced to a point on shoulder; colour white, eroded to 

 purplish grey, interior purple. 



Habitat. In sheltered tidal pool, just sublittoral, under stones on 

 silt; in rock pool with Mytilus in low eulittoral on moderately 

 exposed shore (station 14); dredged from 10-15 m on bottom of silt 

 with scattered pebbles and shells (station 25). To 88 m depth 

 (Powell, 1951). 



RECORDS. Stations 14, 25. Elsewhere above 49°S to Tierra del 

 Fuego (Dell, 1971), extended northward by the present records. 

 Range: 46-54°S. 



Remarks. The brachiopod Magellania venosa was abundant in 

 the dredge samples from station 25, in which both this species and 

 Xymenopsis muriciformis occurred. A few of the brachiopods showed 

 boreholes in their shells, which may have been drilled by one or 

 other of these two muricids. 



Xymenopsis muriciformis (King & Broderip, 1832) 



(Figure 4A) 



Buccinum muriciforme King & Broderip, 1832: 348. 

 Xymenopsis muriciformis - Dell, 1972: 38-39, figs 31, 32 (syn- 

 onymy). Cernohorsky, 1977: 118 (synonymy). Castellanos & 



Landoni, 1993: 16, pi. 3, figs 39, 40. Pastorino & Harasewych, 

 2000: 43-52, figs 1-42, 45^19, 83-95, 105-106 (synonymy). 



Xymenopsis decolor (Philippi, 1845) -Dell, 1971: 212-213. 



Xymenopsis liratus (Gould, 1 849) - Powell, 1951: 158-159. 



Description. Shell to 26 mm; elongate fusiform, with rounded 

 whorls; sculptured by 13-15 rounded axial ribs, crossed by regu- 

 larly spaced incised lines (14-18 on last whorl); apertural lip not 

 thickened; colour white to purplish grey, interior white to purple. 



Habitat. Dredged from 7-15 m, on bottoms of gravel, or cobbles 

 on silt with brachiopods. Dell ( 197 1 ) recorded this species from the 

 sublittoral to 18 m, and Powell (1951) from 17-170 m off the 

 Falkland Islands. 



Records. Stations 14, 22, 25. According to Dell (1971), from 

 about 45°S to Tierra del Fuego. Range: 45-54°S. 



Remarks. This genus shows a confusing diversity of shape and 

 sculpture. Strebel (1904) recognized an improbable 22 species in his 

 'Trophon decolor 1 group. This genus has recently been revised by 

 Pastorino & Harasewych (2000). 



Xymenopsis subnodosus (Gray, 1839) 

 (Figure 4B) 



Buccinum suhnodosa Gray, 1839: 118. 



Xymenopsis subnodosus - Pastorino & Harasewych, 2000: 55-56, 



figs 96-103, 106. 

 Fusus cancellinus Philippi, 1845: 67. Philippi, 1846: 117-118, 



Fusus pi. 3, fig. 2. 

 Xymenopsis cancellinus -Powell, 1951: 158. 



Description. Shell 23 mm; elongate fusiform with shouldered 

 whorls; sculptured with rounded axial ribs (10 on last whorl), 

 crossed by close-set spiral cords, alternately large and small (24 on 

 last whorl); outer apertural lip thickened and denticulate within; 

 colour whitish, anterior canal tinged purple. 



Habitat. Single shell dredged from 5-15 m in sheltered bay, on 

 substrate of cobbles and shells. 



Records. Station 1. The type locality of F. cancellinus is the 

 Magellan Strait (Philippi. 1845). Range: 46-54°S. 



Remarks. Besides the holotype of Philippi's F. cancellinus, this is 

 the only specimen known (Pastorino & Harasewych, 2000). The 

 denticulate lip is unlike other members of the genus. 



Family BUCCINIDAE 



Pareuthria fuscata (Bruguiere, 1789) 

 (Figure 4C) 



Buccinum fuscatum Bruguiere, 1789: 282. 



Pareuthria fuscata -Powell, 1951: 132 (synonymy). 



Pareuthria plumbea (Philippi, 1844) - Powell, 1951: 133. Dell, 

 1971: 207-208 (synonymy). Castellanos, 1992: 13, pi. 3, fig. 37. 



Pareuthria magellanica (Philippi, 1848) -Powell, 1951: 133 (syn- 

 onymy). 



Description. Shell to 30 mm; elongate fusiform; spire whorls 

 sculptured with low, rounded axial ribs, becoming obsolete on last 

 1-2 whorls, otherwise smooth, but sometimes with indistinct spiral 



