NATTCA CLAUSA. 673 



1863 — 85. Natica affinis, Jeffreys, Rep. Brit. Assoc. (Newcastle-on-Tvne), p. 78, 1863 ; in Prestwich, 

 Quart. Journ. Geol. Soc, vol. xxvii, p. 489, 1871 ; Proc. Zool. Soc, p. 35, 1885. 



1870. Natica clausa, Gould, Inv. Mass., ed. 2, p. 342, no. 612. 



1872. Natica affinis, Dawson, Canadian Nat. | n. s.], vol. vi, p. 392, pi. vi, fig. 6. 



1878. Natica clausa, G. 0. Sars, Moll. Reg. arct. Norv., pp. 159, 338, pi. xxi, figs. 12, 13. 



1899. Natica affinis, Posselt, Medd. om Gr0nl., vol. xxiii, p. 142. 



1901. Natica affinis, var. clausa, Brtfgger, Norges geol. Unders0gelse, No. 31, pp. 42, 653, pi. vi, 

 fig. 20 ; pi. xii, figs. 2, 3. 



1901. Natica affinis, Kobelt, Icon, schalentrag. europ. Meeresconcb., vol. ii, p. 84 (pt.), pi. liii, 

 figs. 1—3. 



1910. Natica clausa, 0yen, Krist. Vid. Selsk. Forh., no. 5, p. 27 ; Kgl. Norske Vid. Selsk. Skrift., 

 no. 9, p. 185. 



1910 — 13. Natica clausa, Odlmer, Arkiv. for Zool.., vol. vii, no. 4, p. 7, 1910; K. Svensk. 

 Vet.-Akad. Handl, vol. 1, p. 14, pi. iii, figs. 1-3; 5-14; 16-17 ; pi. v, figs. 7-14. 1913. 



1911. Natica clausa. Yabe, Geol. Mag. [5], vol. viii, p. 212. 



1912. Natica clausa, Dautzenberg et Fiscber, Camp. Scient., Prince de Monaco, vol. xxvii (Mollusques), 

 p. 225. 



1915. Natica (Cryptonatica) clausa, Johnson, Bost. Soc. Nat. Hist., Occ. papers, vol. vii, Faun. New 

 Engl., pt. 13, p. 105. 



Specific Characters. — Shell rather large, fairly strong, globose, imperforate; 

 whorls 5, the last wide, flattened and compressed above, ventricose, much the 

 largest, excavated below ; spire very short, rapidly diminishing to a small point ; 

 suture well marked ; mouth large, semilunar, obtusely angulate above, projecting 

 below ; outer lip expanded, incurved ; inner lip spread over the columella, forming 

 a semi-circular pad covering the umbilicus ; operculum calcareous. 



Dimensions. — Ii. 20 — 25 mm. B. 20 — 25 mm. 



Distribution. — Recent: Circumpolar — Finmark, Lofoten Islands, Iceland, Jan 

 Mayen, Lapland, Spitzbergen, Greenland, Banks of Newfoundland, New England 

 coast, Melville Island, Behring Sea. 



Fossil : Waltonian Crag : Little Oakley. Newbournian : Rams- 

 holt, Sutton. Butleyan : Butley, Alderton, Hollesley. 



Pliocene : Iceland. Pleistocene : Bridlington, Moel Tryfaen. Uddevalla, 

 Christiania fiord. Trondhjem (0yen). Greenland, Labrador. Canada — Montreal, 

 Quebec, Riviere du Loup. Massachusetts. Siberian coast. Japan. 



Remarks. — By many authorities N. clausa and X. affinis have been regarded as 

 varieties of one species; they are evidently allied forms, but I follow Prof. G. O. 

 Sars in considering them specifically distinct. 



The shells I regard as N. clausa are comparatively large and strong, with a 

 wide and expanded base and a short spire, having a northern and circumpolar 

 habitat. Originally figured from specimens obtained in Melville Island during 

 Beechey's voyage, they range, according to Prof. Sars, from Finmark and Spitz- 

 bergen to Greenland and the Behring Sea. N. affinis, on the other hand, is much 

 smaller, narrower, and more fragile, unknown from polar seas, but extending 



