NO. 2094. MOLLVSKfi OF THE GENVB Rlfi^OiyA—BARTHCH. 55 



rounded, short, marked by the continuations of the axial ribs which 

 extend to the umbihcal area. Aperture rather large, sUghtly chan- 

 neled anteriorly and posteriorly; outer hp very thick, reinforced im- 

 mediately behind the edge by a strong varix; inner Hp very thick, 

 somewhat sinuous, appressed to the base. Peristome complete. 



The type and another specimen, Cat. No. 7975, U.S.N.M., come 

 from the Lower Pleistocene of San Diego. The type has 6 whorls 

 and measures: Length, 4.8 mm.; diameter, 1.8 mm. 



RISSOmA CALEFORNICA, new species. 



Plate 33, fig. 1. 



Shell very minute, elongate-conic, semi-translucent, yellowish 

 white. Nuclear whorls 27, weU rounded, smooth. Postnuclear 

 turns well romided, marked by strong, decidedly protractive, shghtly 

 sinuous axial ribs which are about half as wide as the spaces that 

 separate them. Of these ribs 14 occur upon the firet, and 16 upon 

 the remaining turns. These ribs extend strongly from the summit 

 to the sutures on each tiu"n and are not at aU constricted below the 

 summit. The intercostal spaces are deep, well rounded, and smooth. 

 Suture strongly impressed. Periphery of the last whorl well rounded, 

 marked by the continuation of the axial ribs wliich extend over the 

 somewhat prolonged base to the umbihcal chink where they become 

 sUghtly fused on the tumid area surrounding the umbihcal region. 

 Aperture oval; shghtly channeled at the posterior angle and at the 

 junction of the outer Hp and the columella; outer Hp reinforced 

 immediately behind the edge by a thick caUus; columeUa strongly 

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

 a thick caHus which renders the peritreme complete. 



The tj-pe. Cat. No. 271644, U.S.N.M., was dredged in 3 fathoms 

 off South Coronado Island by Doctor Baker. It has 5 postnuclear 

 whorls and measures: Length, 2.8 mm.; diameter, 1.2 mm. Cat. No. 

 271645, U.S.N.M., contains the tip of a yoimg specimen from Cata- 

 lina Island, CaHfornia. 



RISSOINA CLANDESTINA C. B. Adams. 



Plate 32, fig. 5. 



Rissoa dandestina C. B. Adams, Ann. Lye. Nat. Hist. N. Y., vol. 5, 1852, p. 401. 



Shell very smaU, elongate-ovate, yeUowish-white. Nuclear whorls 

 3^, smooth, weU rounded, separated by a well impressed sutm-e. 

 Post-nuclear whorls moderately rounded, appressed at the simamit, 

 marked by protractive, somewhat sinuous, rather strong axial ribs, 

 of wliich 14 occm- upon the first, 16 upon the second and third, and 

 20 upon the penultimate turn. The spaces between the axial ribs 

 are about thi'ee times as wide as the ribs and are smooth. Suture 



