NO. 1'094. MOLLUSKS OF THE GENUS RIS80INA—BARTSCII. 47 



wider at the sutures than at the appresscd summit, marked by very 

 reguhir, moderately strong, pro tractive axial ribs of which 16 occur 

 upon the first, 18 upon the second, 22 upon the third, 24 upon the 

 fourth, 30 upon the fifth, and 32 upon the penultimate turn. These 

 ribs extend prominently to the summit, which they render feebly 

 crcnulated. Intercostal spaces as wide as the ribs, crossed by numer- 

 ous, well-defijied, equal, and equally spaced, incised, spiral lines, 28 of 

 which occur between the sutures on tlie last turn. Sutures feebly im- 

 pressed. Base of last whorl rather long, moderately rounded, marked 

 by thocontmuationsof the axial ribswhich become very much enfeebled 

 on the anterior portion of the base. In addition to the axial ribs, the 

 base is marked with 19 ahnost equal and almost equally spaced spiral 

 threads; these, in conjunction with the axial ribs, give the base a 

 cancellatedly sculptured appearance. Aperture large, channeled ante- 

 riorly and posteriorly; outer lip patulous, very thick, reinforced imme- 

 diately behind the edge by a strong varix ; inner lip moderately thick, 

 sinuous, appressed to the base and so arranged as to lend the aper- 

 ture the aspect of having a partially truncated columella. 



The type and another specimen, Cat. No. 56349, U.S.N.M., come 

 from Cape San Lucas. The type has the last nuclear whorl and 7 post- 

 nuclear turns and measures: Length, 6 mm.; diameter, 1.5 mm. Cat. 

 No. 45156, U.S.N.M., contains another specimen from the Gulf of 

 California. 



RISSOINA ADAMSI, new species. 



Plate 30, fig. 5. 



Rissoa janus var. a. C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, p. 403. 



Shell elongate-conic, bluish-white with a faint narrow, yellowish- 

 wliito band marking the anterior boundary of the posterior tlurd of 

 the spaces between the sutures. Nuclear whorls decollated. Post- 

 nuclear whorls slightly rounded, appressed at the summit, marked 

 by very regular, moderately protractive, slightly curved axial ribs, 

 which are about as wide as the spaces that separate them. Of these 

 ribs, 20 occur upon the second, 26 upon the third, 30 upon the fourth, 

 36 upon the fifth and the penultimate whorl. The shallow inter- 

 costal spaces are crossed by well-impressed spiral lines, of which 

 about 25 occur between the sutures on the antepenultimate whorl. 

 Sutures well impressed. Base short, prolonged, well rounded, 

 marked by the feeble continuation of the ribs on the posterior two- 

 tliirds below the periphery, by about 13 spiral series of pits, wliich 

 are broader and more deeply impressed than those of the spire, while 

 on the extreme anterior portion of the base the spiral lines again 

 become weakened. Aperture large, very oblique, decidedly patulous 

 at the junction of the outer and basal lip. Posterior angle acute ; outer 

 lip very much thickened at the edge. Columella short, with a decided 



