C(ECUM. 183 



regarded as the representative of that shell, is considered 

 by Mr. Clark (whose studious examination of a multitude 

 of individuals of this genus gives much weight to his 

 opinion) as a worn individual of trachea in its produced and 

 arcuated immature condition. 



This species in most respects resembles the C. tracliea. 

 The tentacula, as in the latter, are frosted white and setose, 

 but they appear to be proportionably longer, slenderer and 

 more elevate at the tips ; these variations, however, are 

 scarcely appreciable. The foot is very short, truncate in 

 front, rounded behind, and carried much more laterally in 

 this species than in trachea ; and on its posterior upper 

 part is the most differential point in the animals, the 

 curious operculum, which is circular, and has six or seven 

 spiral gyrations of a pale yellow, but instead of being con- 

 cave or flat without and conical within, as in trachea, it is 

 in both respects the reverse. It is more active in its 

 movements. (Clark.) Through the kindness of Mr. 

 Clark we have examined the living animal, and can bear 

 testimony to the accuracy of his notes. 



The Co?cum glahrum is rare, yet widely distributed. 

 Exmouth, off Budleigh Salterton, six miles from shore, in 

 ten fathoms water (Clark) ; Burrow Island and Guernsey 

 (S. H.) ; Falmouth, Sandwich, Weymouth, Swansea, and 

 adjacent bays, Tenby (Jeffreys). Lerwick in Zetland 

 (Jeffreys). Cork Harbour and Bantry Bay (Jeffreys). 



