56 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



rendered sinuous by the summit of the strong axial ribs. Peri- 

 phery well rounded. Base moderately long, well rounded. Aperture 

 decidedly oblique, oval; posterior angle acute, slightly channeled; 

 outer lip very thick, reinforced by a callus on the outside; colu- 

 mella short, curved, very thick, reflected over and appressed to the 

 base as a very thick callus; parietal wall covered with a thick callus 

 which connect the outer lip and the insertion of the columella. 



Three specimens of this species are in the collection of Amherst 

 College. They were collected by Professor Adams at Panama and 

 served for his description. The one described and figured above 

 has 5 postnuclear whorls in addition to the nucleus, and measures: 

 Length, 3 mm.; diameter, 1.2 mm. 



RISSOINA MEXICANA, new species. 

 Plate 33, fig. G. 



Shell small, narrowly elongate-conic, bluish white, semi- translucent. 

 Nuclear whorls 2, weU romided, smooth, forming a truncated pupoid 

 apex. Postnuclear whorls appressed at the summit, moderately 

 well rounded, marked by well developed, retractive, axial ribs which 

 are about one-half as wide as the spaces that separate them and 

 form continuous series from the apex to the base. Of these ribs 12 

 occur upon the first, 14 upon the second, 16 upon the third and the 

 penultimate turn. Intercostal spaces smooth. Suture slightly 

 wavy, feebly impressed. Base of the last whorl slightly produced, 

 marked by the continuations of the axial ribs which extend promi- 

 nently to the umbilical area. Aperture moderately large, weakly 

 chamicled anteriorly and posteriorly; outer Hp thin mthin where 

 the external sculpture is seen by transmitted light, tliick at the 

 edge and reinforced immediately behind the edge by a strong varix; 

 inner lip tliickened, appressed to the base, rendering the peritreme 

 complete. 



Tlie type. Cat. No. 271G46, U.S.N.M., was collected by the author 

 along the rocky shores at Mazallan. It has 4i postnuclear whorls 

 and measures: Length, 2.7 mm.; diameter, 1.2 mm. Cat. No. 

 15422, U.S.N.M., contains 1 specimen from Guacomayo, Mexico, and 

 Cat. No. 46167, U.S.N.M., 1 specimen from the Gulf "of California. 



RISSOINA BAKERI Bartsch. 

 Plate 33, fig. 4. 

 Rissoinn balceri Bartsch, Nautilus, vol. IG, 1902, p. 9. 



Shell small, sub-diaphanous, milk white. Nuclear whorls 2, 

 quite large, with beveled shoulder, smooth. Postnuclear whorls 

 well rounded, somewhat angulated at the anterior termination of 

 the posterior fourth between the sutures, ornamented hj 12 to 14 



