NO. 1863. M0LLU8KS OF TUE GENUS ALVANIA—BARTSCH. 339 



which 16 occur upon the second and third and 18 npon the penulti- 

 mate turn. These ribs are best shown immediately posterior to the 

 deeply channeled suture, where they appear as a cord of slender 

 tubercles. The main sculpture of the shell consists of fine, spiral 

 lirations, of which 6 occur between the summit and the tubercles on 

 the first turn and 10 upon the second. The space between the 

 tubercles and the suture seems to be marked by a single, spiral 

 liration only. On the last whorl the tubercles are altogether obsolete 

 and the surface of this whorl is marked by 12 subequal and subequally 

 spaced spiral cords, of which the 3 near the summit are the weakest. 

 The spaces between these cords are narrower than the cords. Suture 

 very strongly and deeply channeled. Periphery of the last whorl 

 marked by an impressed groove, which bears a slender, spiral cord in 

 its middle. Base somewhat produced, scarcely rounded, marked b}^ 

 eight equal and equally spaced, spiral cords. Aperture very oblique, 

 rather large, oval; posterior angle acute; outer lip decidedly thick- 

 ened immediately behind the thin edge; inner lip stout, curved, 

 reflected over, and appressed to the base; parietal wall covered with 

 a thick callus which joins the posterior angle of the aperture with the 

 columella and renders the peritreme complete. 



The specimen described and figured is one of ten (Cat. No. 208500, 

 U.S.N. M.), which come from the Gulf of California. It has four post- 

 nuclear whorls and measures: Length 2.8 mm., diameter 1.3 mm. 

 Cat. No. 16207, U.S.N.M., contains one specimen from Cape San 

 Lucas, Lower California, and Cat. No. 32368, U.S.N.M., contains two 

 from the Gulf of California. 



ALVANIA TRACmSMA, new species. 

 Plate 29, fig. 7. 



Shell elongate-ovate, yellowish white. (Nuclear whorls decol- 

 lated.) Post-nuclear whorls slightly rounded, marked by slender, 

 well roimded, almost vertical, axial ribs, of which 26 occiu* upon the 

 first and second and 22 upon the third and the penultmiate turn. 

 These axial ribs are about one-third as wide as the spaces that sep- 

 arate them and extend prominently from the summit of the whorls, 

 where they terminate in rounded cusps, to the umbilical area. In 

 addition to the axial sculpture, the whorls are marked by spiral 

 cords, of which 3 occur between the sutures on the first and second 

 whorls, 5 on the third, and 6 on the penultimate turn. The spiral 

 cords pass over the axial ribs as cords. The spaces inclosed between 

 the axial ribs and the spiral cords are elongate oval pits, having 

 their long axes parallel with the spiral scidpture. Suture broad and 

 very deeply channeled. Periphery of the last whorl marked by a 

 sulcus a little wider than those occurring on the spire, crossed by the 



