Cyclostrema, Adeorbis, Vitrinella, cmd related genera. 127 



Circulus trilix Bush. 



Skenea trilix Bush, Expl. Albatross, Report U. S. Com. Fish and Fisheries for 188.3, 

 p. 584, 1885. 



yo)i Homalogyra densicosta Tryoii, Manual, ix, p. 399, pi. 61, figs. 10-11, 1887. 



Adeorbis supranitidus Dall, Bull. Mus. Comp. Zool , xviii, p. 278, 1889; Bull. U. S. 

 Nat. Mus., No. 37, p. 150, pi. xli, figs. 7, 7a, 1889, in part. 



Plate XXII. figs. 6, 10, 10a and 12, a-g. Plate XXIII. figs. 10 and 15. 



The most common species of this genus off Cape Hatteras, N. C, 

 in V-17 fathoms, 1883-1884. 



The opercuhim of trilix is thin, horny, circular, of about five 

 whorls with central nucleus. The animal matter, the shell having 

 been removed with nitric acid, is too much dried to dissect but 

 shows stout tentacles, prominent eyes situated at their bases, and 

 a rather broad, bilobed snout (fig. 6). The radula, although ex- 

 tremely minute, measuring about •3'"'" in length and •I'"™ in width, 

 reveals interesting characters and shows that this species unques- 

 tionably belongs to the Rhiphidoglossa. The radula (fig. 12) con- 

 sists of between 50 and 60 rows of teeth ; in each row there is a 

 comparatively wide central tooth (fig. (7) having a base with convex 

 sides and bearing a long, finely serrated, strongly pointed hook; on 

 either side a narrow, long, lateral tooth (fig. e) with a serrated hook ; 

 and beyond twenty or more delicately pointed, sickle-shaped, mar- 

 ginal ones (figs, f, g). These were revealed only when exceed- 

 ingly high power objective and oculai*, of a magnifying power 

 of about 1000 diameters, were used, and even then only the higher 

 lines could be seen; when using a lower power of about 500 diame- 

 ters, only ten of the marginal hooks could be counted. See p. 128. 



Circulus supranitidus ("Wood) Jeffreys. 



Adeorbis supranitidus Wood, Ann. Mag. Nat. Hist., ix, p. 530, 1842; Crag Mol- 

 lusca, p. 137, pi. XV, figs. 5, a-b, London, 1848. 



Circulus Duminyi Requien, var. supranitidus Jeffreys, B. C, iii, p. 315, 1865. 



Adeorbis siqyranitidus Jeffreys, P. Z. S., London, p. 42, 1885. 



I^on Omalaxis supranitida G-. 0. Sars, Moll. Reg. Arct. Norv., p. 214, pi. 22, figs, 

 20 a-b, 1878=(0. (?) Sarsi sp. nov.) 



Non Adeorbis supranitidus Dall. Bull. Mus. Comp. Zool., xviii, p. 278, 1889; Bull. U. 

 S. Nat. Mus., N"o. 37, p. 150, pi. xli, figs. 7, 7a, 1889. 



Plate XXIIL figs. 1 and 2. 



Through the courtesy of Mr. Dall, I have been able to study two 

 authentic specimens of siqyranitidus from the Crag, in the U. S. 

 National Museum. 



