332 Mr. A. Adams on new Mollusca from Japan. 



Monograph of Pleurotoma. They are small, mitriform, plicate 

 species, with a narrow-linear aperture, and with the last whorl 

 contracted at the fore part. 



Zafra mitriformis, A. Adams. 



Z. testa mitriformi, in medio incrassata, alba, fascia fusca obscura ad 

 suturas ornata, anfractu ultimo ad basin rufo tincto, et linea an- 

 gusta rufa transversa ad peripheriam circumcincto ; anfractibus 6§, 

 planiusculis, longitudinal iter plicatis ; plicis validis, obliquis, sub- 

 distantibus ; anfractu ultimo antice constricto et oblique sulcato. 



Hab. Mino-Sima; 63 fathoms. 



Genus Rissoella, Gray. 



The little shells I propose to describe as species of this genus 

 agree with it as at present constituted, and all have the appear- 

 ance of being adult. They may, however, as may those also 

 from the British Seas, be the young of other genera, But until 

 we are in a position to demonstrate their real nature, or until, 

 by an examination of the animal, they are proved to be only a 

 transition state in the metamorphoses of some higher Mollusca, 

 it is desirable to record their existence in every sea investigated. 

 Numerous small shells, evidently nuclear whorls of known ge- 

 nera, have been rejected from my list, some being immature 

 Macrocheili and Odostomics, and others the embryonic state of 

 larger Gasteropods. 



1. Rissoella omphalotropis, A.Adams. 



R. testa conoidali, alba, opaca, profunde umbilicata ; umbilico can- 

 nula circumcincto ; anfractibus 3£, convexiusculis, suturis pro- 

 fundis, anfractu ultimo ad peripheriam vix angulato, transversim 

 obsolete exarato ; apertura subcirculari, antice vix producta ; labio 

 rectiusculo, subincrassato. 



Hab. Sado ; 30 fathoms. 



2. Rissoella vitrina, A. Adams. 



R. testa conoidali, anguste umbilicata, solidiuscula, vitrea, pellucida ; 

 anfractibus 3j,leevibus, convexiusculis, ultimo rotundato,ventricoso, 

 suturis marginatis ; umbilico angusto, simplici ; apertura orbicu- 

 lari. 



Hab. Tabu-Sima ; 25 fathoms. 



3. Rissoella vesicalis, A. Adams. 



R. testa globoso-conoidea, rimate umbilicata, alba, semiopaca; an- 

 fractibus 3£, convexis, lsevibus, suturis profundis, simplicibus, an- 

 fractu ultimo rotundato, ventricoso ; apertura circulari ; labio 

 brevi, rectiusculo, sup erne subdilatato. 



Hab. Sado; 30 fathoms. 



