SYSTEMATIC 119 



Genus Falsilunatia n.g. 

 Type: Natica soluta Gould, 1848 



On shell and opercular characters soluta is not dissimilar from catena Da Costa, the Recent English 

 genotype of Lunatia, but the dentition is most distinctive. 



In catena the radula is normal for the family — a tricuspid central tooth of more or less rectangular 

 form, laterals with three or four cusps and the inner marginal with a side cusp, thus approximating the 

 bifid form. In soluta the central tooth is hemispherical with a large, broadly triangular central cusp but 

 merely vestigial side cusps. The laterals have a broad massive cusp with a slight incision or incipient 

 denticle near the base of its inner margin. The marginals are simple, not bifid, the outer one the longer. 



The umbilicus is narrower than in Lunatia and may be open or closed according to the relative 

 downward encroachment of the parietal callus. 



Falsilunatia soluta (Gould) 



Natica soluta Gould, 1848, p. 239. 



Natica soluta Tryon, 1886, p. 39, pi. 9, fig. 71. 



Natica soluta Strebel, 1906, p. 138, pi. 11, figs. 61, 62 and 64-66. 



Natica soluta Strebel, 1908, p. 60. 



Type locality. Southern coast of South America. 

 St. 48. 8-3 miles N 53 E of William Point Beacon, Port William, Falkland Is., 3 May 1926, 105-115 m. 

 St. 51. Off Eddystone Rock, East Falkland Is., 4 May 1926, 115 m. 

 St. WS 244. West of Falkland Is., 52° 00' S, 62 40' W, 18 July 1928, 247 m. 



St. WS 808. Between Falkland Is. and Patagonia, 49° 40' 15" S, 65 42' W, 8 Jan. 1932, 109-107 m. 

 St. WS 817. Between Falkland Is., and Patagonia, 52 23' S, 64 19' W, 14 Jan. 1932, 191-202 m. 



Dentition. Fig. J, 47, p. 192. 



Strebel (loc. cit. 1907) subdivided his material, on the size of the umbilical cavity, into forms 'A', 

 ' B ' and ' C '. Forms A and C. are here covered by soluta typical, but form B, which equals Mabille 

 & Rochebrune's recognita, I consider to be specifically separable on account of the spreading of the 

 parietal callus pad, which results in the closing of the umbilicus from above and a disproportionate 

 thickening and flexing of the columellar callus. 



Falsilunatia recognita (Rochebrune & Mabille) 



Natica recognita Rochebrune & Mabille, 1889, p. H 33. 



Type locality. Orange Bay, Patagonia, 120 m. 

 St. WS 766. Between Falkland Is., and Argentina, 45 13' S, 59 56' 30" W, 18 Oct. 193 1, 545 m. 



Dentition. Fig. J, 48, p. 192. The radula is very similar to that of soluta, but presents minor differences 

 in the shape of the central tooth, which is narrower and more acutely arched, and in the laterals, which 

 have a shorter cusp and the addition of several denticles. The inner basal plate of the central tooth is 

 strengthened by two massive vertical processes, which, when viewed laterally, are shown to act as 

 buttresses. The marginals are simple as in soluta. 



A similar style of central tooth is found in the New Zealand genus Globisinum (Powell, 1933, p. 170) 

 (Fig. J, 49) and in Natica fartilis Watson (1881), from between Marion Island and Prince Edward 

 Island in 50-140 fathoms. 



Apart from radula similarities, Falsilunatia differs from Globisinum in having an animal that is 

 completely retractive and a smaller, more solid shell. The animal in the New Zealand G. venustum 

 Suter resembles that of Sinum in being much larger than the shell, but it is not known if an operculum 

 is normally present. The operculum in Natica fartilis is shelly. 



