PHOLAS. DIMY ARIA. 115 
corresponds with Solen siliqua. The others are separated under different 
generic appellations. 
The Solens inhabit the ocean, concealing themselves in sand. 
But few fossil species have been found, and these occur in the London Clay, 
and Calecaire-grossier of France. 
‘Genus LIV. ~PHOLADOMYA. — Sowerby. 
Generic Character.— Shell transverse, inequilateral, 
equivalve, ventricose, very thin and hyaline, anterior side 
more or less elongated and gaping; posterior side, some- 
times very short, rounded; upper edge slightly gaping ; 
hinge with a small, rather elongated triangular pit, and a 
marginal lamina in each valve; to the outer surface of 
which is attached a somewhat short external ligament ; 
inside pearlaceous; two indistinct muscular impressions, 
muscular impression of the mantle nearly obsolete, and 
with a large sinus, 
Pholadomya angustata. Plate IX. fig. 19. P. lirata. 
Plate IX. fig. 23. 
" The P. candide@ is the only recent species of the genus known, it is found on 
the coast of the Island of Tortola. The umbones are so close to each other, 
that they are worn through by the attrition of opening and shutting of the 
valves. 
The shells of this genus-partake of the characters of Anatina and Pholas, 
but may be distinguished from them by the external ligament; and the want 
of accessory valves; in the structure of the hinge they are allied to Panopza, 
but differ in their extreme thinness, transparency, and pearly texture; and 
from Mya, in wanting the unequal teeth of that genus. 
Fossil species are pretty numerous, and occur in the Inferior Oolite, Corn- 
brash, Fuller’s Earth, the London Clay, Lias, and the Sutherland coal-field. 
TRIBE IIlI.— PHOLADARIA. 
Shell bivalve, with accessory pieces to the valves ; gaping 
much anteriorly. 
Genus LV. — PHOLAS. — Linneus. 
Generic Character. — Shell transversely oblong, equivalve, 
greatly inequilateral ; nearly the whole species gaping at 
both ends, and most of them with the opening very large at 
the anterior end, and extending along the basal margin; in 
some species, however, it is nearly closed by a testaceous, 
almost smooth, somewhat tubular prolongation of the 
valves; hinge in various species with au unequally sized small 
recurved tooth in each valve ; external surface generally 
roughened with muricated striz, presenting a rasp or file- 
like appearance; most of the species provided with a 
