264 
November 11, 1851. 
W. J. Broderip, Esq., Vice-President, in the Chair. 
Professor OwEN read a paper “On the Capacity of the Cranium 
in the Negro, the Orang, and the Gorilla,” which will be published 
in the Transactions of the Society for the present year. 
The following papers were also read :— 
1. DerscripriIONS OF SIXTEEN NEW SPECIES OF RISSOINA, A 
Genus or Marine Gasteropopous MOoLuusks, FROM THE 
CuminGian Coxtitection. By ArtHuR ADAMS, SURGEON 
R.N., F.L.S. etc. 
Rissorna, D’Orbigny. 
About eighteen species of this genus, as restricted by M. d’Or- 
bigny, have been already described, inhabiting various countries. 
Those here named are a portion of the discoveries made by Mr. Cu- 
ming among the islands of the Philippine Archipelago, and are many 
of them of considerable size; and it is in these that the peculiarity 
of operculum is best seen. 
The process of the semiovate, horny, subspiral operculum, first 
pointed out by D’Orbigny, is sometimes very long and slender, and 
very much resembles in appearance the analogous appendage of the 
operculum of Nerita and Neritina. The genus Jeffreysia of Alder, 
or Rissoella of Gray, has a similar appendage, but the position of 
the eyes, and the peculiar structure of the fore part of the head, 
place the latter genus in a different family, viz. Pyramidellide. The 
Rissoine may also readily be known from the neighbouring genus 
Rissoa, by the aperture being somewhat channeled anteriorly, whereas 
in Rissoa it is continuous and entire. The nature of the animal re- 
sembles Rissoa, according to D’Orbigny, who places the genus 
among the Melaniade. 
1. Rissorna puicata, A. Adams. R. testd turrito-subulatd, 
subpyramidali, albd, sordidd, anfractibus octo, planis, longi- 
tudinaliter valde plicatd, transversim striatd, plicis elevatis, 
postice subangulatis, interstitiis transversim striatis ; aperturd 
semiovatd, antice subcanaliculatd ; labro anticé subdilatato, 
margine incrassato. 
Hab. Isle of Masbate. Mus. Cuming. 
2. Rissorna rascrata, A. Adams. R. testd subulato-turritd, 
solidd, sordidé albd, rufo-fusco fasciatd, anfractibus octo, con- 
vexiusculis, transversim tenuissimé (sub lente) striatd, longitu- 
dinaliter plicatd, plicis obliquis, equalibus, subdistantibus ; 
aperturd semiovatd, anticé subcanaliculatd ; labro subdilatato. 
Hab. Sydney, under stones, low water (Mr. Strange). Mus. 
Cuming. 
