NO. 2094. M0LLU8K8 OP THE 0ENU8 RISSOn^A—BARTSCH. 39 



species. It lacks the strong basal callus resulting from the reflection 

 of the columella, and also the thickened lip. See plate 32, fig. 4. 



Professor Adams's shells are at Amherst College, Massachusetts. 

 The United States National Museum contains three lots of this spe- 

 cies: Cat. No. 4163, 1 specimen from the Cape of San Lucas; Cat. 

 No. 46151, 3 specimens from the Gulf of California, and Cat. No. 

 222865, 3 specimens from Cape Pulmo, Gulf of California. 



RISSOINA EXCOLPA, new species. 

 Plate 30, fig. 2. 



Shell elongate-conic, semitransparent, bluish white. Nuclear 

 whorls decollated, except the last turn, which is smooth. Post- 

 nuclear whorls moderately well rounded, appressed at the summit — 

 which creeps up on the preceding whorl — marked by sublamellar, 

 somewhat sinuous, protractive, axial ribs, which are about one-third 

 as wide as the spaces that separate them and form continuous lines 

 from whorl to whorl. Of these ribs, 12 occur upon the first and 14 

 upon each of the remaining turns. In addition to the axial ribs, the 

 whorls are marked in the intercostal spaces by exceedmgly fine lines 

 of growth which, combined with the spiral sculpture, lend the surface 

 of the shell a very minutely reticulated appearance. The spiral sculp- 

 ture consists of numerous, fine, spiral lirations, which are about as 

 wide as the spaces that separate them. Of these lirations, 28 occur 

 between the sutures on the penultimate turn. Suture moderately 

 constricted. Periphery of the last whorl well rounded. Base some- 

 what produced anteriorly, well rounded, marked by the strong con- 

 tmuations of the axial ribs which extend to the anterior end of the 

 shell, the spiral sculpture of the base being in every way similar to 

 that on the spire. Aperture irregularly oval; posterior angle acute; 

 outer lip thick, reinforced by a strong varix; columella short, stout, 

 strongly curved and decidedly reflected over and adnate to the base; 

 parietal wall covered with a thick callus, which renders the peritreme 

 complete. 



The type and two other specimens. Cat. No. 46155, U.S.N.M., come 

 from the Gulf of California. The type has 5+ post-nuclear whorls and 

 measures: Length, 4.1 mm.; diameter, 1.8 mm. Cat. No. 23748, 

 U.S.N.M., contauis 2 additional specimens from the Gulf of California. 



RISSOINA STRICTA Menke. 

 Plate 28, fig. 6. 

 Rissoina stricta Menke, Zeit. f. Malak., 1850, p. 177, No. 37. 



Shell large, elongate-conic, bluish white. Nuclear whorls at least 

 2, well rounded, smooth, forming a well elevated helicoid spire. Post- 

 nuclear whorls flattened, weakly shouldered at the summit, marked 

 by strong, slightly curved, decidedly protractive axial ribs of which 



