40 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



12 occur upon the first, 14 upon the second, 16 upon the thh'd, IS 

 upon the fourth, 20 upon the fifth, 22 upon the sixth, 26 upon the 

 seventh, and 28 upon the penultimate whorl. These ribs extend 

 prominently to the summit and render the sutures crenulated. Inter- 

 costal spaces almost as wide as the ribs, crossed between the sutures 

 by numerous very fine, closely spaced, spiral striations. Base of the 

 last whorl moderately long, well rounded, marked by the continua- 

 tions of the axial ribs which extend undiminished to the umbilical 

 chink and by 15 equal, and equally spaced, slender, spiral threads 

 which extend prominently across the intercostal spaces and weakly 

 over the ribs. Aperture small, very oblique, channeled anteriorly 

 and posteriorly; outer lip very thick, reinforced immediately behind 

 the edge by a strong varix; inner lip moderately thick, appressed to 

 the base, sinuous, the anterior portion so arranged as to give the 

 aperture the aspect of having a truncated columella. 



Cat. No. 4062, U.S.N.M., contains 3 specimens from Cape San Lucas, 

 1 of which has served for our description and figure. This has lost 

 the first IJ nuclear whorls, retaining only 1 of them. It has 9 post- 

 nuclear whorls and measures: Length, 8.7 mm.; diameter, 3.3 mm. 



The following specimens are in the collection of the United States 

 National Museum: 



Cat. No. 4062, Cape San Lucas, Lower California, 3 specimens; 

 Cat. No. 34209, La Paz, Lower California, 4 specimens; Cat. No. 

 46153, Gulf of California, 2 specimens; Cat. No. 46157, Gulf of 

 California, 2 specimens; Cat. No. 46163, Mulege Bay, Lower Cali- 

 fornia, 2 specimens; Cat. No. 46168, Gulf of California, 1 speci- 

 men; Cat. No. 76269, Mazatlan, Mexico, 1 specunen; Cat. No. 

 195370, St. Margarita Island, Lower California, 1 specimen; Cat. 

 No. 222864, Cape Pulmo, Lower California, 9 specimens; Cat. No. 

 264297, south end of Tiburon Island, Gulf of California, 2 speci- 

 mens; Cat. No. 264979, San Josef Island, Gulf of California, 12 speci- 

 mens; Cat. No. 264990, Agua Verde Bay, Gulf of California, 14 speci- 

 mens; Cat. No. 266657, San Francisquito Bay, Gulf of California, 3 

 specimens; Cat. No. 267154, San Francisquito Bay, Gulf of California, 

 12 specimens; Cat. No. 271616, Mazatlan, Mexico, 5 specimens. 



RISSOINA FORTIS C. B. Adams. 



Plate 29, figs. 5, 6. 



Rissoafortis C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, p. 402. 



Shell large, elongate-conic, milk-white. Nuclear whorls smooth, 

 well romided, separated by constricted sutures. Post-nuclear whorls 

 flattened in the middle, roundly shouldered at the summit, marked 

 by very regular, slightly sinuous, moderately protracted, well rounded 

 axial ribs, of which 12 occur upon the first, 14 upon the second, 18 



