NO. 2094. M0LLUSK8 OF THE GENUS RI880INA—BARTSCH. 45 



axial ribs whicti are about one-half as broad as the spaces that sepa- 

 rate them. Of these ribs, 12 occur upon the first, 14 upon the second, 

 16 upon the third and fifth, 18 upon the sixth, 20 upon the seventh 

 and penultiraate turn. These ribs extend prominently to the sum- 

 mit, rendering the suture sinuous. Intercostal spaces marked between 

 the sutures by numerous exceedingly fine, closely spaced, spiral stria- 

 tions. On the later turn a few of the coarser basal threads appear 

 immediately above the suture. Base moderately long, marked by 

 continuations of the axial ribs, which extend prominently to the 

 umbihcal chink, where they become somewhat fused, forming a basal 

 fasciole. The spiral structure of the base consists of about 15 threads, 

 which pass over the intercostal spaces and the axial ribs. The 

 spaces separatmg these threads are almost equal to the threads in 

 width. Aperture small, oblique, auricular, slightly channeled ante- 

 riorly and posteriorly. Outer hp thin at the edge, reinforced imme- 

 diately behind the edge by a strong varix. Inner lip thick, appressed 

 to the base, free only at the extreme anterior margin, connecting 

 with the outer lip at the posterior margin and rendering the peritreme 

 complete. 



The type and another specimen. Cat. No. 46161, U.S.N.M., come 

 from the Galapagos Islands. The type has 9 postnuclear whorls 

 and measures: Length, 9 mm.; diameter, 3.5 mm. Cat. No. 56348, 

 U.S.N.M., contains another specimen from the same locahty. 



RISSOINA DINA, new species. 

 Plate 29, fig. 4. 



Shell medium size, elongate-conic, yellowish white. Nuclear 

 whorls decollated. Postnuclear whorls moderately rounded, feebly 

 shouldered at the summit, marked by strongly rounded, somewhat 

 sinuous, pro tractive axial ribs of which 12 occur upon the first, 14 

 upon the second, 16 upon the third and fourth, 18 upon the fiftti, 

 22 upon the sixth and the penultimate turn. These ribs extend 

 prominently to the summit of the whorls, rendering the suture 

 smuous. Intercostal spaces about one and one-half times as wide 

 as the ribs, marked between the sutures by exceedingly fine spiral 

 striations. Base moderately long, marked by the continuations of 

 the axial ribs, which extend prominently to the anterior portion of 

 the base passing over the well-expressed fasciole. The spiral sculp- 

 ture of the base consists of 16 low, broad cords which pass over the 

 intercostal spaces and the ribs, appearing on the latter as overlap- 

 ping tiles, the free edge being directed posteriorly. Aperture very 

 oblique, small, auricular, channeled anteriorly and posteriorly; outer 

 lip very thick within, reinforced immediately behind the edge by a 

 strong varix; inner lip very thick, appressed and adnate to the base 

 throughout its entire length. 



