VARIETIES OF OYSTERS. l8l 



Var. suborbtcularis. Shell larger, with the slope much 

 higher than usual, and considerably narrower behind : 



O -> 



ears smaller. Length cry, breadth 0*7. 



HABITAT : Cornwall (Hockin). F. Monte Mario 

 (Rigacci) ; E. Mediterranean electric-telegraph cable, at a 

 depth of over 1000 f. (Milne-Edwards). Shetland, Skye, 

 Larne (co. Antrim), Birterbuy Bay (co. Galway), Guernsey 

 (J. G. J.) ; Exmouth (Clark); in gravelly sand, 18-80 

 fathoms. It is a rare species. The variety is remarkable. 

 . The foreign range of P. Testa extends from 

 Norway to Algeria and the ^Esrean This 



j O O 



beautiful species differs from P. tigrinus, with which it is 

 sometimes found, in the following particulars :--The shell 

 is broader, flatter, and thinner ; the ribs, when they occur, 

 are scaly or prickly ; the punctures are very strongly 

 marked, and arranged in squares ; the beaks are much less 

 prominent, and raised ; the ears are not so unequal ; and 

 the inside margin is seldom crenulated. Forbes and 

 Hanley considered it to be a variety of P. striatus ; but 

 Malm has satisfactorily shown some of the points of differ- 

 ence between these two species. There is no intermediate 

 form. P. Testa has, indeed, some of the sculpture of P. 

 tigrinus and the shape of P. striatus, but the colouring of 

 the first is more bright and vivid than that of the other 

 two. Some specimens are perfect gems. 



7. P. STRIATUS, Miiller. 



P. striatus, Mull. Zool. Dan. Prodromus, p. 248, No. 2994 > 

 F. and H. 2, p. 281, pi. 51, f. 1-4, and (animal) pi. S. f. 2. 



BODY whitish, irregularly streaked lengthwise with 

 opaque white lines : mantle edged with white, and having 

 an outer fringe of extensile white cirri : ocelli 25 in num- 



