HETEROPHROSYNID.E. 55 



as local varieties. The Rissoa rubra of Macgillivray is 

 certainly the present species, and not Barleeia rubra as 

 he supposed. 



Family X. HE'TEROPHROSY'NID^E, Clark. 



BODY spiral : mantle plain-edged : head snout-shaped : ten- 

 tacles cylindrical and short, with rounded tips : eyes sessile, or 

 nearly so : foot double-edged in front ; hinder part of the sole 

 slightly grooved down the middle. 



SHELL small, conical, and spiral : operculum not spiral hut 

 increasing by concentric layers, with the nucleus on the inner 

 side, next to the pillar ; that side is strengthened by a rib, and 

 furnished underneath with a spike -like process or plate, which 

 projects from the nucleus. 



As the name imports, these mollusks are abnormal, 

 allied to the Littorinidce, and distinguishable from that 

 family not much more than the Turbinidce are from the 

 Trochidoe*. The operculum is very peculiar. It has 

 an excentric nucleus, like that of Buccinumj and an in- 

 ternal process analogous to that of Neritina. 



Although the appellation given by Mr. Clark 19 a 

 long one, it must in justice and on other grounds be 

 preferred to either of those subsequently proposed by 

 Dr. Gray, viz. Rissoellidae and Barleeiadce. In the sys- 

 tem of the latter author these families are separated 

 by Cuaplida and several others. 



The Heterophrosynida are not restricted to the At- 

 lantic Ocean : Dr. P. Carpenter has described some from 

 the Pacific. They inhabit the laminarian zone, and ap- 

 pear to be gregarious. 



* See vol. iii. p. 337. 



