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 64, 
planiusculis, longitudinaliter plicatis ; plicis validis, obliquis, sub- 
distantibus ; anfractu ultimo antice constricto et oblique sulcato, 
Hab, Mino-Sima; 63 fathoms. 
Genus Rissoriia, 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 Odostomia, and others the embryonic state of 
larger Gasteropods. 
1. Rissoella omphalotropis, A. Adams. 
R. testa conoidali, alba, opaca, profunde umbilicata; umbilico cari- 
nula circumcincto ; anfractibus 33, 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 34, levibus, 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 34, convexis, leevibus, suturis profundis, simplicibus, an- 
fractu ultimo rotindato, ventricoso; apertura circulari; labio 
brevi, rectiusculo, superne subdilatato. 
Hab. Sado; 30 fathoms. 
