\o. 1826. MOLLUSKS OF THE GENUS BITTIVM—BABTSCH. 401 



BITTIUM (LIROBITTIUM) INTERFOSSA Carpenter. 



Plate 51, figs. 2 and 6. 



Rissoa interfossa Carpenter, Rep. Brit. Ass. Adv. Sci. for 1863, 1864, p. 656. 

 Cerithiopsis fortior Carpenter, Rep. Brit. Ass. Adv. Sci. for 1863, 1864, p. 660. 

 Cerithiopsisfortior Carpenter, Ann. Mag. Nat. Hist., ser. 3, vol. 15, 1865, p. 337. 

 Rissoina interfossa Carpenter, Proc. California Acad. Nat. Sci., vol. 3, 1866, 

 p. 217. 



Shell rather large and robust, white, sometimes light brown. 

 Nuclear whorls small, two; the first obliquely tilted, smooth; the 

 second with two strong spiral cords which divide the space between 

 the sutures into three equal areas. Post-nuclear whorls appressed 

 at the summit, strongly slopingly shouldered, ornamented with two 

 strong spiral keels, which divide the space between the sutures into 

 three equal areas, and very strong, vertical, axial ribs, 16 of which 

 occur upon each of the turns. The intersections of the axial ribs 

 and the spiral cords form strong elongated tubercles, the long axes 

 of which coincide with the spiral sculpture. These tubercles slope 

 more abruptly posteriorly than anteriorly. The intersections of 

 the axial ribs and the spiral cords inclose shallow squarish pits. 

 Sutures weakly impressed. Periphery of the last whorl marked 

 by a strong keel to which the axial ribs extend feebly. This keel 

 is a little nearer to the first post-peripheral keel than that is to its 

 posterior neighbor. Base moderately long, marked by two very 

 strong keels, which divide the space between the peripheral keel 

 and the tip of the columella into three equal areas, the spaces between 

 the keels being very deep and a little wider than the keels. Entire 

 surface of spire and base, including the ribs and intercostal spaces, 

 crossed by numerous, fine, closely spaced, spiral striations. Aper- 

 ture irregular, channeled anteriorly; posterior angle obtuse; outer 

 lip thick within, thin at edge, rendered sinuous by the external 

 sculpture; columella stout, strongly twisted, and reflected; parietal 

 wall glazed with a thick callus. 



The specimen described and figured is one of a lot (Cat. No. 56906, 

 U.S.N.M.) from Catalans Island, California, the type-locality. It 

 has nine post-nuclear whorls, and measures: Length 8.3 mm., diame- 

 ter 3.1 mm. The type is a much -worn young specimen having 

 seven post-nuclear whorls, and measuring: Length 6.2 mm. 



80796°— Proc. N.M. vol. 40—11 26 



