42 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



immediately behind the edge by a strong varix; imier lip thin, sinu- 

 ous, appressed to the base, the anterior ]^ortion is so arranged as to 

 give the aperture the appearance of having a truncated columella. 

 Peritreme complete. 



The type and 15 specimens, Cat. No. 46158, U.S.N.M., come from 

 Pearl Island, Panama. The type, a pei-fect specimen, has 8 post- 

 nuclear whorls, and measures: Length, 7 mm,; diameter, 3 mm. 

 Cat. No. 23331, U.S.N.M., contains 3 specimens from the same place. 

 Cat. No. 204118, U.S.N.M., contains 2 specimens from Perico Island, 

 Bay of Panama. Cat. No. 272936, U.S.N.M., 7 specimens from 

 Panama. 



RISSOINA INCA D'Orbigny. 



Plate 31, figs. 6, 8. 



Rissoina inca D'Orbigny, Voy. Amer. Merid., 1840, p. 395, pi. 53, figs. 11-16. 



Shell broadly conic, yellowish white, with a pinkish suffusion. 

 Nuclear whorls smooth. Postnuclear whorls shouldered at the 

 summit, which is rendered wavy by the axial ribs. Axial ribs strong, 

 sinuous, about half as wide as the deep spaces that separate them. 

 Of these ribs, 10 occur upon the first, 12 upon the second and third, 

 14 upon the fourth, and 16 or 17 upon the last whorl. These ribs 

 extend prominently from the summit of the whorls to the umbilical 

 area. The intercostal spaces are marked by fine spiral striations. 

 Sutures rendered sinuous by the strongly developed ribs. Base well 

 rounded, marked by a continuation of the axial ribs and strongly 

 incised spiral cords, of which more than 15 are present. Aperture 

 ear-shaped; outer lip reinforced immediately behind the edge by a 

 thick callus; columella somewhat twisted and deflected; parietal 

 wall covered with a thick caUus, which renders the peritreme 

 complete. 



The type has 6 postnuclear whorls, and measures: Length, 8 mm.; 

 diameter, 3 mm. 



The species was collected by D'Orbigny in the neighborhood of 

 Arica, Peru, and Cobija, Bolivia. 



I have copied the figure given by Gustav Schwartz von Mohren- 

 stern, in his monograph on the Family Rissoidae Besons. Abdr., vol. 

 19, Denksch. Math. Naturw. Class, Kais. Akad. Wissensch., p. 40, 

 pi. 1, fig. 1, 1860, which gives more detail than Orbigny's origmal 

 figure, which is a rather poor drawmg. Mohrenstern says that 

 Orbigny had found this species very abundant and had collected more 

 than 1 ,000 specimens of it, and had been very generous in the distri- 

 bution of his material. 



This species is the type of the genus Rissoina, which was established 

 by Orbigny in the same work in which he gives status to the present 

 form. 



