46 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 49. 



The type and two other specimens, Cat. No. 56350, TJ.S.N.M., come 

 from the Gahipagos Islands. The type has 8 postnuclear whorls and 

 measures: Length, 7 mm.; diameter, 3 mm. 



RISSOINA EXPANSA Carpenter. 



Plate 28, fig. 5. 



Rissoina expansa Carpenter, Ann. and Mag. Nat. Hist., ser. 3, vol. 15, 1865, 

 pp. 399-400. 



Shell broadly conic, bluish white, semitranslucent. Nuclear whorls 

 decollated. Postnuclear whorls increasing rapidly in size, much 

 broader at the sutures than at the summit, which is almost ap- 

 pressed; marked by low, broad, axial ribs which are less elevated and 

 much wider at the periphery of the whorls than, at the summit. Of 

 these ribs, 16 occur upon the first, 18 upon the second and third, 22 

 upon the fourth, and 24 upon the penultimate turn. On the last two 

 turns, these axial ribs become obsolete a little posterior to the 

 periphery, leaving a narrow, smooth band in the sutures and on the 

 posterior half of the base of the last whorl. The intercostal spaces 

 are triangular in shape, being broader at the summit and narrowing 

 at the suture, or periphery in the case of the last whorl. These spaces 

 are not quite as wide as the ribs and are crossed by numerous, fine, 

 spiral striations. Base inflated, well rounded, shghtly concaved an- 

 teriorly, marked by very feeble continuations of the axial ribs which 

 are scarcely more expressed than lines of growth and about 13 spiral 

 cords which are situated on the anterior half of the base growing grad- 

 ually weaker from the anterior portion of the base to the middle. 

 Aperture very oblique, strongly channeled anteriorly and posteriorly; 

 outer lip thick, claw-shaped; inner lip moderately thick, sinuous, 

 strongly appressed to the base and so arranged as to give the aper- 

 ture the aspect of having a truncated columella. 



Doctor Carpenter's type, Cat. No. 15954, U.S.N. M., comes from 

 Mazatlan, Mexico. It has lost the nucleus and probably the first 

 2 postnuclear turns. The 5 remaining measure: Length, 9.1 mm.; 

 diameter, 4.7 mm. Cat. No. 59339, U.S.N.M., contains 2 specimens 

 from Acapulco. Cat. No. 271642, U.S.N.M., 1 specimen from Guay- 

 mas, the latter a perfect specimen in every way excepting the lost 

 nucleus. The 2 early postnuclear whorls in this have 14 and 16 axial 

 ribs respectively. The spiral sculpture is a little more strongly ex- 

 pressed on the early whorls than on the succeeding turns. 



RISSOINA PENINSULARIS, new species. 

 Plate 29, fig. 1. 



Shell of medium size, elongate-conic, bluish white, semitranslucent. 

 Early nuclear whorls decollated, one only remaining which is smooth. 

 Postnuclear whorls increasing very regularly in size, flattened, much 



