44 THE MOLLUSCA OF THE FIRTH OF CLYDE. 
Drébak (Jeffreys), Denmark (fHellebvk), Gibraltar and Vigo 
(M‘Andiew), Naples (Costa), Algiers (Weinkauff). 
SAXICAVA, Plewrian de Bellevue. 
* Savicava rugosa, Linné. 
Mytilus rugosus, Linné; Mya byssifera, Fabricius ; Hiatella 
rugosa, Hleming. Variety arctica = Mya arctica, Linné, 
and Hiatella arctica, Lamarch. 
Habitat—The type, as well as the variety, is common 
everywhere from a little above low tide to all depths, 
in the crevices of stones and rocks, the roots of large 
seaweeds, and the cavities or whorls of dead shells; large 
and fine specimens are, however, scarce. My largest 
measures 1;°5 by 7 of an inch, and is from Mountstuart, 
Bute. The varieties are endless, and have given rise to an 
extensive synonymy. 
British distribution —Throughout all parts of our seas ; 
exceedingly common. 
Foreign localities—From Spitzbergen (Haton) and Ice- 
land (Verkriizen), throughout northern and western Europe, 
and as far as Mogador and the Canaries (Andrew) ; also 
throughout the Mediterranean. In America it occupies the 
west coast as far south as Mazatlan (Carpenter), and the east 
as far as New Bedford, as well as the Arctic seaboard, the 
variety arctica having been found by Captain Feilden in 
81° 41’ N. lat. It is said to inhabit also the Antarctic seas ; 
and Mr. Jeffreys states that specimens from Australia cannot 
be distinguished from those from Greenland, except that 
they are smaller. 
FAMILY PHOLADIDA, Gray. 
Pholas, Linné. 
* Pholas crispata, Linné. 
Pholas bifrons, Da Costa ; Pholas crispus, Gmelin. 
Habitat.—Gregarious in indurated clay, at Rothesay Bay, 
Ardbeg Point,and Ardmaleish Point, Bute; Millport Bay, Cum- 
brae, near the quay; Campbeltown Loch, north side; in soft 
clay—RBogany shore, Bute ; and Balloch Bay, Cumbrae. Mr. 
Norman, who reports it in loose pieces of “ shale” from Lam- 
lash Bay, makes the following remark—“ It usually bores 
from beneath upwards, and when it has perforated the stone 
through to the upper side . . . it dies.” This species is 
