[TAYLOR] MARINE MOLLUSCA 31 
Whiteaves gives the dimensions of a specimen dredged by Dr. Dawson 
in Alert Bay at 12 X 11 X 75 mm., and I have a shell slightly larger 
even than this.! 

According to Dr. Dall’s arrangement, which we are following, the 
suborder Waiadacea will come in here. We have two species of this 
order, of course inhabiting fresh water, and belonging to the family 
Unionide. They are : 
27. ANODONTA NUTTALLIANA, Lea, 
28. MARGARITANA MARGARITIFERA, Linne, sp. 
AXIN AA, Poli. 
29. AXINÆA SEPTENTRIONALIS, Middendorff, sp. 
Pectunculus septentrionalis, Midd., Mal. Ross., pt. iii., p. 67, pl. xxi., fig. 1-3 (1849), 
var.— A. subobsoleta, Cpr., Rept. Brit. Assoc., 1863, p. 644 (Aug., 1864); and 
Ann. Mag. Nat. Hist., 3rd series, vol. xiv., p. 425 (Dec., 1864). 
This species does not occur in the neighbourhood of Victoria, so far 
as I have observed. It is found, however, not uncommonly on the 
western and northern coasts of Vancouver Island and at the Queen 
Charlotte Islands. (Dawson.) 
Our shell is the A. subobsoleta of Carpenter, but its specific identity 
with the septentrionalis of Middendortff is doubted by some conchologists. 
NUCULA, Lamarck. 
30. NucuLA CASTRENSIS, Hinds. 
Proc. Zool. Soc. London, 1843, p. 98; and Zool. Voy. Sulph., vol. ii., p. 63, pl. xviii., 
fig. 5 (1844), = N. Lyalli, Baird, Proc. Zool. Soc. London, 1863, p. 71. 
This shell, which is undoubtedly the N. Lyalli of Baird, and almost 
certainly the JV. castrensis of Hinds, is the commonest bivalve shell 
occurring in our seas. In Departure Bay last year I dredged more than 
2,000 specimens of it in one day. Dr. Dawson dredged it at the Queen 
Charlotte Islands and in many localities to the north of Vancouver 
Island. 

' Since writing the above I have had occasion to examine the description and 
figures of the true C. decussata of the Atlantic, and I find that our British Colum- 
bian shells do not belong to that species at all. Mr. Whiteaves, in his account of 
Dr. Dawson’s collections, has twice recorded our shells as C. decussata, and as the 
species had already been found on the Californian coast, I suppose we accepted his 
determination of the shell without question. Our species may be C. faba, O. Fab., 
but unfortunately I cannot at this moment refer to either descriptions or specimens 
of this species. 
