152 LITTORINIDiE. 



vision. The lower tentacles may be considered to repre- 

 sent the lobes of the muzzle in Eissoa, here elongated into 

 tentacles, and covered with vibratile cilia in the same 

 manner with the upper pair : these latter are more flat- 

 tened and broader than in Rissoa. 



" The operculum is very peculiar. The projecting in- 

 ternal plate I do not recollect to have observed in any 

 other genus, though the spine in Nerita approaches to it. 

 It appears from the ridges on its inner surface to afford 

 attachment to a muscle. 



" Jeffrey sia is a littoral genus, found in company with 

 Rissoa on small sea-weeds in pools between tide-marks. 

 Its alliance is evidently with that genus, which in the 

 shell, it so strongly resembles ; and the lingual armature 

 bears out the affinity, differing but little from that of 

 Rissoa interrupta and some of the commoner species. 

 Some others of the small transparent shells usually in- 

 cluded under Rissoa^ may probably, when they are obtained 

 alive or with the operculum, be found to belong to this 

 genus." * Alder, in Litt. 



J. DiAPHANA, Alder. 

 Oblong conic ; whorls at least four ; body less than the spire. 



Plate LX XVI. fig. 1. 



Rissoa glabra, Brown, lUust. Conch. G. B. p. 13, pi. 9, f. 37 ? 

 Rissoa ? glabra. Alder, Ann. Nat. Hist. vol. xiii. p. 325, pi. 8, f. 1, 2, 3, 4. 

 „ Jiaphana, Alder, Cat. Moll. Northumb. and Durh. p. 55. 



The name glabra was applied to this species by Mr. 

 Alder, under the impression, that what he had previously 



* This account of a most interesting and distinct new genus has been entirely 

 communicated by our valued friend Mr. Alder. 



