BIVALVIA. 283 
In the living state it has been only obtained in deep water. 
A small obtuse tooth occupies a position immediately beneath the umbo in the 
living shell, but in the fossil this is merely rudimentary. 
The figure by Middendorff has the siphonal side the larger. 
2. PANoPEA Fausasui, Menard de la Groye. Tab. XXVII, fig. 1, a—/. 
Panopna Fausasit. Men. dela Groye. Ann. du Mus., tom. ix, p. 131, t. 12, 1807, 
— — Dubois de Montp. Conch. Foss. de Wolhyn. Podol., p. 51, pl. 4, 
figs. 1—4, 1831. 
Panopma Favsasit. Bast. Foss. de Bord., p. 95, 1825. 
— — Bronn. Leth. Geog., p. 973, pl. 37, fig. 6, 1838. 
— — Phil. En. Moll. Sic., vol. i, p. 7, t. 2, fig. 3, 1836. 
— — Goldf. Pet. Germ., vol. il, p. 274, t. 159, fig. 1, a—d. 
— — Valenciennes. Arch. du Mus., vol. i, p. 13, 1839. 
— —- J. Sow. Min. Conch., t. 602, figs. 3—5. 
— — Chenu. Conch. Ilust., pl. 4, fig. 1, 1. 
= Iesviciensis. J. Sow. Min. Conch., t: 611, figs. 3, 4. 
— — Valenciennes. Loc. cit. sup., No. 36. 
_ REFLEXA. Say. Journ. Acad. Nat. Sc., vol. iv, p. 153, pl. 13, fig. 4, 1824. 
= — Conrad. Foss. Med. Tert., p. 5, pl. 3, fig. 4, 1838. 
_— Americana. Id. Foss. Med. Tert., p. 4, pl. 2. 
— AutprovanDi! Phil. En. Moll. Sic., vol. i, p. 7, t. 11, fig. 2. 
— GENTILIS. J. Sow. Min. Conch., vol. vii, t. 610, fig. 1, 1840. 
Mya Panop#a? Broce. Conch. Foss. Subap., p. 532, 1814. 
Spec. Char. Testa transversd, ovato-oblongd, inflatd ; plus minusve inequilaterali ; 
postice truncatd et valde hiante ; cardine unidentato. 
Shell transverse, ovately oblong, inflated, more or less inequilateral; posterior side 
truncated, and gaping widely; binge with one tooth. 
Length, 6 inches. Height, 33 inches. 
Locality. Cor. Crag, Sudbourn, Gedgrave, Ramsholt. 
Red Crag, Sutton. 
This handsome shell is very abundant as a Crag Fossil, though its great size and 
comparative thinness has caused it to be somewhat scarce in our Cabinets: at 
Ramsholt numerous specimens were found with the valves united. It presents a very 
considerable variation, both in regard to its form, and to the degree of gape on the 
anterior side, and I am inclined to believe the recent Mediterranean shell called 
P. Aldrovandi is merely the descendant of our Crag species somewhat altered by 
local conditions: the Sicilian fossil (specimens of which were obligingly given to me 
by Madame Power) seems to present some differences; but they are not, I think, of 
sufficient importance for specific distinction; that shell is, in general, rather more 
inequilateral than the Crag one, but not always so; and, among my British specimens 
