BIVALVIA. 255 
Fragments of this species are by no means rare, and pervade the whole of the Red 
Crag Deposit. The specimen figured is one of a pair of valves found in situ at Walton 
Naze, but in a very fragile condition, and much reduced in substance. The fragments 
from Suffolk display, generally, a greater solidity in the anterior portion, which is 
that most commonly obtained. f 
Much importance has been placed upon differences in proportional dimensions. 
In this, the length is about five times that of its height, while in S. si/iqua some speci- 
mens are as one to eight. The greatest difference appears to be in the impression of 
the margins of the mantle; in this it is more inward, or further from the anterior edge, 
and, on the contrary, the more linear shell (S. s/igua) has the impression nearer the 
extremity, with a slight difference also m the form of the anterior adductor. The 
truncation of this extremity generally forms an angle of about 95°, but this is not 
constant; and I am inclined to believe (although they are here separated in deference 
to the recent conchologists, who have better materials to work upon) that the two 
forms are merely varieties of one and the same species, the differences of locality and 
other conditions producing all the variations shown by the two shells.* 
2. SoLEN sILIQqua, Linnaeus. Tab. XXV, fig. 7, a—e. 
Sozen sttraua. Linn. Syst. Nat., ed. 12, 1113, No. 34, 1767. 
— — Poli. Test. Sicil., vol. i, pl. 10, figs. 7—11. 
— _— Turt. Brit. Biv., p. 80, pl. 6, fig. 5, 1822. 
— — Phil. En. Moll. Sic., vol. i, p. 4; vol. ii, p. 5. 
— — Forb. and Hanl. Hist. Brit. Moll., vol. i, p. 246, pl. 14, fig. 3. 
— ovacuLa. Mont. Test. Brit., p.47, 1803. 
— cua. Turt. Brit. Biv., p. 82, pl. 6, fig. 6. 
— masor. List. Hist. Conch., lib. ii, fig. 255. 
Spec. Char, Testa lineari, recta, levigatd ; extremitate subtruncaté non marginata ; 
in valva sinistrad unidentato, in alterd bidentato ; dentibus lateralibus elongatis. 
Shell linear or cylindrical, straight and smooth; extremity truncated, not mar- 
ginated ; one cardinal tooth in the left valve, and two in the other; lateral teeth 
elongate. 
Length, 5 inches. Height, ? inch. 
* It is possible that a portion of the Red Crag of Suffolk may have been derived from the destruction 
of the Older or Coralline Crag Formation, intermixed with the exuvize of animals belonging to the seas of the 
former period, as well as with other extraneous fossils. The cliff at Walton Naze, however, affords strong 
presumptive evidence that the whole of the Red Crag is not derivative, and that the animals whose remains 
are there deposited, lived and died in the spot where they are now found. Bivalves are frequently obtained 
in this locality with the two portions united, and it seems scarcely possible that such a specimen as the 
above could have been removed out of one Formation to have been deposited, with its two fragile valves 
in their natural position, in the mud or sand of a succeeding period. 
