122 DISCOVERY REPORTS 



Genus Tectonatica Sacco, 1890 



Type (monotypy) : Natica tectula Bonelli, Pliocene, Italy 



Tectonatica impervia (Philippi) PI. X, fig. 62 



Natica impervia Philippi, 1845 a, II, fig. 6. 



Natica impervia Hupe (Gay), 1854, p. 221. 



Natica impervia Tryon, 1886, p. 31, pi. 9, fig. 66. 



Natica impervia Rochebrune & Mabille, 1889, p. H 34. 



Natica impervia Strebel, 1906, p. 134, pi. XI, fig. 60. 



Natica impervia Strebel, 1908, p. 61. 



Natica impervia Melvill & Standen, 1912, no. 18, p. 348. 



Type locality. Strait of Magellan. 



St. 51. Off Eddystone Rock, East of Falkland Is., 4 May 1926, 105-115 m. 



St. 159. Off South Georgia, 53 52' 30" S, 36 08' 00" W, 21 Jan. 1927, 160 m. 



St. WS 795. North of Falkland Is., 46 14' S, 6o° 24' W, 18 Dec. 193 1, 157-161 m. 



St. WS 838. Between Falkland Is. and Strait of Magellan, 53 11' 45" S, 65° 00' 00" W, 5 Feb. 1932, 148 m. 



These shells are characterized by a massive funicle which fills the umbilicus and is defined on its 

 outer edge by a crescentic grove. The operculum is white and calcareous except for a thin horny layer 

 on the inner side. The exterior is smooth, without sulci. The ' Discovery ' examples have been compared 

 with Falkland Islands material from the British Museum. 



Strebel (1908) described a var. major from Paulet Island, 100-150 m., but I have not seen examples. 



Dentition. Fig. J, 46, p. 192. The radula conforms in general features with that most commonly 

 found in Naticoids. The central tooth is tricuspid, but the side cusps are much shorter than the central, 

 which reaches right to the basal margin. The laterals have a large centre cusp with a very weak one on 

 each side. The inner marginal is simple, long and slender, the outer shorter, more robust and bifid at the 

 tip, a reversal of the usual arrangement, for in all other instances known to me it is the inner marginal 

 that is the bifid member. 



Several authors (Dall, 1892; Woodring, 1928; Finlay & Marwick, 1937) have synonymized Crypto- 

 natica Dall, 1892 (type Natica clansa Brod. & Sowb.), but the dentition of this Arctic species does not 

 conform with that of impervia. In clausa (Troschel, 1861, pi. 14, fig. 14), the central has a single large 

 cusp and the marginals are both simple. 



Since the radula and opercular features are unknown quantities for the Pliocene genotype of 

 Tectonatica, I am at present justified only in disassociating impervia from Cryptonatica. 



Range. Strait of Magellan (type) ; Tierra del Fuego, 36 m. (Strebel) ; off Falkland Is., 105-161 m. ; 

 Burdwood Bank, Falklands area, 56 fathoms (Melvill & Standen) ; South Georgia ; Paulet I., 100-150 m. 

 (var. major). 



Family LAMELLARIIDAE 



Genus Lamellaria Montagu, 18 15 



T ,, . • c »u Type : Lamellaria perspicua Linn. 



Lamellaria patagonica Smith Jr r r 



Lamellaria patagonica Smith, 1881, p. 32, pi. 4, figs. 9, ga, gb. 

 Lamellaria patagonica Rochebrune & Mabille, 1889, p. H 36. 



Type locality. Trinidad Channel, 30 fathoms, Patagonia. 

 St. 56. Sparrow Cove, Port William, East Falkland Is., 16 May 1926, 10.V-16 m. 



One example only, easily recognized by the dirty yellow ground colour of the mantle, which is lined 

 and blotched with Vandyke brown, as described by Smith. 



