54 PROCEEDINGS OF THE NATIONAL ]\[178EUM. vol.40. 



Cat. No. 105574, U.S.N.M., contains 9 specimens from the same lo- 

 cality. Cat. No. 105560, U.S.N.M., 2 specimens from San Ignacio 

 Lagoon. Cat. No. 105545, U.S.N.M., 2 specimens from Scammons 

 Lagoon. 



RISSOINA EFFUSA MSrch. 

 riate 32, fig. 7. 

 Rissoina effusa ^loRcn, Mai. Bliitt., vol. 7, 1860, p. 67. 



Shell small, elongate-conic, yellowish white, tr;inslucent. Of the 

 nuclear whorls the last volution only remains, the first hah of which 

 is well romided and smooth, while the second half bears a small, 

 acute spiral keel on its middle. Postnuclear whorls strongly, slop- 

 ingly, shouldered at the summit, marked by very flexuous, strong, 

 acute axial ribs, of which 10 occur upon the first, 12 upon the second, 

 14 upon the third, and 16 upon the remaining whorls. These ribs 

 extend prominently over the shoulder at the simimit where they 

 take a protractive cm've which emphasizes decidedly the sinuosity 

 of the ribs. Tlie intercostal spaces arc strongly impressed and about 

 thi-ee tunes as wide as the ribs. Sutm-es moderately constricted. 

 The periphery of the last whorl well rounded, base somewhat pro- 

 longed, well rounded, marked by the continuation of the axial ribs 

 which extend prominently to the callus at the end. Aperture mod- 

 erately large, irregularly ovate, feebly channeled anteriorty and 

 posteriori}' ; outer lip moderately thick at the edge, reinforced im- 

 mediately behind the edge by a strong varix; iimer lip twisted and 

 strongly curved, strongly reflected over and appressed to the base 

 in the form of a callus; parietal wall covered by a thick callus which 

 rendei^s the peritreme complete. The entire peritreme is heavier in 

 this shell than in any other we have seen from the west coast. 



Our description and figure have been based upon the type which 

 was kindly loaned to us by Lli*. Ad. Jensen of the Zoological Museum, 

 of Copenhagen. The type has 6 postnuclear whorls and measures: 

 length, 4.S mm. ; iliameter, 1.9 mm. Locality, Central America, with- 

 out specific designation. 



RISSOINA PLEISTOCENA, new species. 



Plate 32, fig. 2. 



Shell small, elongate-ovate, yellowish white. Nuclear whorls de- 

 collated. Postnuclear whorls well rounded, appressed at the siun- 

 mit, mai-ked by very strong, distantly spaced, lamelliform, pro- 

 tractive, axial ribs which form continuous series from the apex of 

 the shell to the base. Of these ribs 12 occur upon the first to third 

 whorls and 14 upon the remaining turns. Intercostal spaces a little 

 more than three times as wide as the ribs, smooth. Suture moder- 

 ately impressed, rendered wayj by the strong axial ribs. Base well 



