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. Descriptions of sixteen new species of Rissoina, a 

 GENUS OF Marine Gasteropodous Molltjsks, from the 

 CuMiNGiAN Collection. By Arthur Adams, Surgeon 

 R.N.,F.L.S. etc. 



Rissoina, 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. Pyramidellidce. The 

 RissoincB 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 Melaniadee. 



1. Rissoina plicata, A. Adams. R. testd turrito-subulatd, 

 suhpyramidali, albd, sordidd, anfractihus octo, planis, longi- 

 tudinaliter valdh plicatd, ti'ansversim striatd, plicis elevatis, 

 postice subangulatis, interstitiis transversim striatis ; aperturd 

 semiovatd, antick subcanaliculatd ; labro antici subdilatato, 

 margine incrassato. 



Hob. Isle of Masbate. Mus. Cuming. 



2. Rissoina fasciata, A. Adams. R. testd subulato-turritd, 

 solidd, sordidd albd, rufo-fusco fasciatd, anfractibus octo, con- 

 vexiusculis, transversim tenuissime {sub lente) striatd, longitu- 

 dinaliter plicatd, plicis obliquis, cequalibus, subdistantibus ; 

 aperturd semiovatd, antice subcanaliculatd ; labro subdilatato. 



Hob. Sydney, under stones, low water (Mir. Strange). Mus. 

 Cumihg. 



