SYSTEMATIC 151 



That the Muricids and Thaisids are more closely interrelated than is generally supposed would seem 

 to be indicated by the dentition. On shell and opercular characters there is little to distinguish the 

 South Georgian Trophon shackletoni pancilamellatus from the Magellanic T. laciniatus, but whereas the 

 former has a radula typical of most Trophons that of the latter closely agrees with the rather distinctive 

 type found in the Thaisid genus Stramonita and also in certain of the Drup a-like genera. The similarity 

 would appear to be too strong to be accounted for by mere coincidence. This type of radula differs from 

 that of the remaining members of the family in having well-developed denticles along the outer edge of 

 the side cusps of the central tooth. 



I am not suggesting that on the one-sided evidence of the radula only one family should be admitted, 

 for it seems that the characters of both the operculum and the columella afford a satisfactory differentia- 

 tion that is in accord with general shell characters. 



It is yet to be satisfactorily explained to what extent the radula can become modified to suit different 

 feeding methods. In cases where a shellfish, presumed to have been an active feeder, has developed 

 a ciliary method, the response appears to be a reduction of the radula to vestigial and functionless size 

 rather than a radical change in the form and arrangement of the teeth. This has apparently occurred in 

 Trophon echinolamellatus (described below), a shell of equal size to that of the genotype, Trophon 

 geversianus, but with a radula that is many times smaller than that of the second named species. 



Genus Trophon Montfort, 18 10 

 Type (o.d.) : Trophon magellanicus Gmelin ( = geversianus Pallas) 

 The genus Trophon is well developed in the southern ocean and has its counterpart in Boreotrophon 

 of Arctic and North Temperate seas. Typical Trophon has a large globose thin shell with prominent 

 axial lamellae and a smooth paucispiral asymmetrical protoconch. The radula consists of a central tooth 

 with an L-shaped lateral on each side. The central tooth is broad and shallow with three main cusps 

 and two intermediates. Operculum horny, ovate with a terminal nucleus. 



Trophon geversianus (Pallas) 



Buccinum geversianus Pallas, 1769, p. 33, pi. 3, fig. I. 



Murex magellanicus Gmelin, 1792, p. 3548, no. 80 (excl. var. B). 



Murex magellanicus Dillwyn, 1817, p. 725. 



Murex lamellosus Dillwyn, 1817, p. 730. 



Murex magellanicus Wood, 1818, p. 132, pi. 26, fig. 90. 



Murex patagonicus, magellanicus and varians d'Orbigny, 1841, pp. 451-4- 



Trophon geversianus Gould, 1852, p. 227, pi. 6, fig. 227. 



Fusus geversianus (Gay) Hupe, 1854, p. 167. 



Trophon geversianus Tryon, 1880, p. 144, pi. 32, figs. 337-34°- 



Trophon geversianus Rochebrune & Mabille, 1889, p. H53. 



Trophon geversianus Strebel, 1905 a, p. 173, pis. 4-6. 



Trophon geversianus Smith, 1905, p. 334. 



Trophon geversianus Melvill & Standen, 1907, p. 106. 



Trophon geversianus Strebel, 1908, p. 37, pi. 6, fig. 94a, b. 



Trophon geversianus Melvill & Standen, 1914, p. 120. 



Type locality. Strait of Magellan. 

 St. 56. Sparrow Cove, Port William, East Falkland Is., il cables N 50° E of Sparrow Point, 16 May 1926, 



105-16 m. 

 St. 58. Port Stanley, East Falkland Is., 19 May 1926, 1-2 m. 



St 1230 67 miles N 62 W from Dungeness Lt., Magellan Strait, 23 Dec. 1933, 27 m. 

 St. WS 847. Off Santa Cruz, Patagonia, 50° 18' 45" S, 67 44' W, 9 Dec. 1932. 56-84 m. 



