244 MARSHALL: ADDITIONS TO 'BRITISH CONCHOLOGY,' 



half-way to Faroe, and as the above dredgings were nearer our 

 coast than to the Faroes, it follows that this should be recognised 

 as a British species. It does not settle the point to say that it 

 is a ' cold area ' and has an arctic or semi-arctic fauna. It is 

 either in British waters or it is not. And if we had a ' cold 

 area' between England and Ireland, or between England 

 and the Channel Islands, English naturalists would claim the 

 fauna of that area, arctic notwithstanding. This is a noteworthy 

 point, as it affects other species besides the present one. 



A short description of the shell appears in 'B. C.,' vol. ii., 

 p. 64, under the synonym of P. sulcatus Miill., and a good 

 figure is given in Jeffreys' Supplementary Plates, as well as in 

 Sowerby's Index. 



P. opercularis van audouinii Payr. Differs from the type 

 in having three rows of prickles or imbrications — one on 

 the summit, and another on each of the sides. It is also 

 a longer shell proportionally. An excellent figure is given 

 in Sowerby's Index, Guernsey, rare. 

 P. vitreus Chem. Described in Appendix to ' B. C.,' and 

 figured in Supplementary Plate, but for some reason not 

 included in Mr. Somerville's List. Besides a valve found 

 by Dr. Edmondston in Shetland, it has also been taken 

 between the Hebrides and Faroes in 530 fathoms. 

 Mytilus edulis var. flavus Poli. Shell straw coloured, and 

 smaller. Found by Miss Hockin at Newquay, Cornwall, 

 on floating wood. This is the variety named in Somer- 

 ville's List var. pallida Marsh. MS. ; but Poli long ago 

 described a light-yellow form as var. flavus. 

 M. modiolus var. gigas Norm. I find this varietal name 

 in ' Museum Normanianum,' but do not know if it has 

 been described. It is quite applicable, however, to our 

 large Dogger Bank form, which sometimes exceeds nine 

 inches in length. 

 M. modiolus var. cylindrica Marsh. Smaller, of a more 

 equal breadth throughout, the margin being less prominent 



J.C, vii., Oct. 1893. 



