286 MOLLUSCA FROM THE CRAG. 
Saxicava PHoLaDIs. Turt. Brit. Biv., p. 21, t. 2, figs. 11, 1822. 
— — Hancock. Mag. Nat. Hist., vol. xvili, p. 337. 
— DistorTA. (Say.) Gould, Inv. Massach., p. 61, fig. 40. 
—_ suLcATA. Smith. Phil. Trans., 1835, pl. 2, fig. 25. 
PuoLEopra RuGosA. Leach. Ross’s Voy. Baff. Bay, p. 174, 1819. 
BrapHo.us rucosus. Leach MS. An. and Mag. Nat. Hist., vol. xx, p. 272. 
ByssoMyA PHOLADIS. Bowdich. Bivalves, fig. 43. 
RHOMBOIDES RUGOsUS. Blainv. Man. Malac., p. 573, 1825. 
HIATELLA OBLONGA. Turt. Brit. Biv., p. 25, pl. 2, fig. 13, 1822. 
— Rveosa. Flem. Brit. An., p. 461, 1828. 
Spec. Char. Testa variabile, oblonga, vel subrhomboidali transversim. striata, rugosa ; 
utraque eatremitate obtusd, aliquando valvarum angulis binis instructo: latere antico 
brevissimo. 
Shell variable, oblong or subrhomboidal, transversely striated, and rugose; obtuse 
or rounded at each extremity ; sometimes furnished with two diverging rows or slightly 
imbricated ridges ; anterior side much the shorter. 
Length, 1 inch. Height, 2 inch. 
Locality. Cor. Crag, Sutton. 
Red Crag, Sutton, Walton Naze. 
Clyde Beds, Bridlington. 
Recent, Britain, Mediterranean, Scandinavia, N. E. Coast of America, 
Nova Zembla, Sea of Ochotsk, and Sitka. 
Small specimens of this shell are abundant in the Cor. Crag. In the Red Crag 
they are sometimes met with, in loose sand, with the valves united, much distorted, and 
with a large, ventral opening. The gigantic specimens obtained in the Clyde Beds, 
and in the recent Deposits of Canada, belong, I believe, to nothing more than a variety 
of this species, where, apparently under favorable circumstances, it had attained to so 
great a magnitude; but one of my specimens from the Red Crag is not much less, 
giving every reason to suppose the simple difference in size, if not merely a difference 
in age, may be the result of different conditions ; the Red Crag specimens bearing in 
yeneral a sort of intermediate character, as if a reduction in temperature from the 
older to the more modern Periods had been favorable to the fuller development of 
this species. 
Large numbers of individuals are found loose in the Crag, and when in a living 
state, probably passed their lives in adhering by a byssus to the roots of Muci. Mr. 
Sowerby, in ‘Min. Conch.,’ speaks of a specimen having been found imbedded in 
Septaria, beneath the Red Crag at Holywells. I have never met with the British 
fossils otherwise than in localities where, I believe, they were not excavators. This 
species appears to be generally distributed through the Drift Beds in this country, and 
it is also found in similar Deposits in Canada, Sweden, and Russia. Mr. Smith, of 
Jordan Hill, has recently forwarded to me the drawing by the late Professor E. Forbes, 
