VENUS. 347 



because of its tendency to vary. Although the general 

 shape and colouring are the same, an endless diversity 

 occurs. In young and half- grown specimens of the 

 variety laminosa the edges of the ribs at the sides are 

 sharp and prickly, as in V. Casina. In adult examples 

 of the variety gibba the crenulations on the inside mar- 

 gin are apt to become more or less obliterated. I have 

 one from Oban which is twisted and inequivalve. 



Availing myself of the candid admission made by the 

 authors of the ' British Mollusca/ that " it is perhaps a 

 matter of controversy whether the Venus gallina of Lin- 

 naeus is specifically distinct from the one so designated 

 by the British writers/' I have reunited with that spe- 

 cies the Pectunculus striatulus of Da Costa. The only 

 difference that I can detect between the shells from the 

 Mediterranean and our own coasts is, that the former 

 have usually (but not invariably) a purplish-brown stain 

 inside at the posterior extremity ; this I cannot regard 

 as a sufficient mark of distinction. The only other 

 points of comparison indicated by Forbes and Hanley 

 are common to both forms, as will appear from a critical 

 examination of the characters given in my description 

 of the species and several varieties. Linne named the 

 northern form in his ' Fauna Suecica 9 V. gallina ; and 

 although, in the tenth edition of his ' Systema Naturae/ 

 he mentions the Mediterranean only, in the more com- 

 plete and universally recognized edition (the twelfth) he 

 first cites the l Fauna Suecica ' and then says, " Habitat 

 in M. Mediterraneo, Norvegico, Asiatico." His diagnosis 

 would include both the northern and southern forms. 

 Miiller, in his ' Zoologise Danicse Prodromus/ describes 

 the Scandinavian shell as V. gallina. I am aware that, 

 according to Deshayes, the siphonal tubes in specimens 

 which he examined on the Algerine coast are much 



