194 COOKE : NOTE ON CONCHOLEPAS PERUVIANUS. 



It would be interesting to trace the steps by which so re- 

 markable a genus as Concholepas became derived from Pur- 

 pura, and by which the operculum, as the mouth grew in size, 

 gradually gave up the attempt to cover it. In the only other 

 Purpuroid which, for size of mouth relative to the whole shell, 

 bears any comparison to Concholepas, viz., Monoceros muricatum, 

 the operculum is very large and of the normal type, covering 

 the entire mouth. I collected a few living specimens of this 

 rare shell at Panama, in 1879, at extreme low water mark of an 

 unusually low spring-tide. 



The present position of the operculum of Concholepas 

 would seem to be, in a certain sense, protective. The animal 

 feeds on Mytilus edtilis^ which, with M. Magellanicus, abounds 

 on the Chilian coasts. In order to enable the proboscis to 

 work with most effect, viz., more or less at right angles to the 

 bivalve attacked, the hinder (or spire) end of the shell must be 

 slightly elevated. When this is done, the operculum forms a 

 sort of fence or barricade, covering the soft parts which would 

 otherwise be exposed. 



LAND SHELLS OF GIBRALTAR. 



By J. H. PONSONBY. 



At page I. of vol. iv. of this Journal will be found a list, 

 published by Dr. Kobelt in 1883, of the land shells of Gibraltar. 

 This was supplemented by a further list, published in 1885 (see 

 page 226, vol. iv., of this Journal), in which the number of 

 species was brought up to twenty-seven. 



A recent visit to the Rock has enabled the following 

 additions and alterations to be made, and even now it would 

 not be safe to predict that the subject is by any means 

 exhausted : — 



J.C, v.,°July, 1887, 



