28 PKOCEEDINGS OF THE ACADEMY OF [Jan., 



intervals smooth. Whorls about S, moderately convex, the last with 

 a very strong, heavy varix behind the outer lip, and with a convex 

 siphonal fasciole at the base, bounded above by a groove and regularly 

 plicate, the ribs passing over it. Aperture semioval. the outer lip 

 thick and sinuous, columellar margin but slightly concave, a shallow 

 but distinct channel at its base in the basal margin. 



liCngth 4.8, diam. 2 mm. 



Kamakura, Sagami. Types No. 70,906, A. N. 8. P. It also occm's 

 at Hahajima, Ogasawara, No. 1,3906 of Mr. Hirase's collection. 



This form is related to R. costulata Dkr., but differs by its more num- 

 erous ribs. R. plicatula Gld., an unfigured species, also seems to be 

 related. 



Kissoina (Zebina) tridentata (Michaud). 



Rissoa tridentata Michaud, Descript. nouv. esp. Rissoa (p. 6) in Ann. Soc. 



Linn, de Lyon, I, 1836. 

 Rissoina curta Sowb., Schwartz, Monogr. Rissoina, p. 107 (1860). 

 R. bidentata Phil., Archiv. f. Naturg., 1845, p. 64 (^Friendly Is.). 

 R. eulimoides A. Ad., P. Z. S., 1851, p. 279 (Capul, Philippines). 

 Eidima dentiens Dkr., Malak. Bl., XVIII, 1871, p. 152 (Viti Is.). 

 Rissoa crassilabnnn Garr., Proc. Cal. Acad., I, 1857, p. 102 (Hilo). 

 Rissoina coronata Reel., Schwartz, Monogr. Rissoina (1860), p. 109 (Mauri 



tius) . 



Kikai-ga-shima, Osumi, typical specimens of this species, which has 

 not before been reported from the east coast of iVsia. The synonymy 

 as given by Tryon" requires some emendation in the light of the large 

 series of specimens now available for study. The following forms, 

 united with R. tridentata b}'' him, are, in my opinion, perfectly distinct 

 species : 



Rissoa semiglabrata A. Ad., P. Z. S., 1851, p. 279. 



Rissoa semiplicata Pse., P. Z. <S., 1862, p. 242 : Ainer. Jour, of Conch., 

 Ill, p. 295, PL 24, fig. 29. 



The former of these differs from all forms of tridentata in the more 

 acuminate spire and the sculpture. The latter, of which specimens 

 from Pease are before me, is a yQYj much smaller species, with more 

 of the spire plicate. I add to the synonymy of R. tridentata the Eidima 

 dentiens of Dunker, of which authentic specimens are before me. It 

 is absolutely identical with tridentata Mich. R. crassilabrum Garrett 

 is also a typical tridentata, with teeth, and 8 mm. long. 



Whether the toothless form coronata ' Reel.' Schwartz is varietally 

 separable is doubtful, but the series before me shows that toothless 

 individuals occur with normal tridentata. The size varies a good deal: 



Length 5.3, diam. 2.3 mm. (Schwartz, type of R. coronata). 



" Man. Conch., IX, p. 389. 



