BIVALVIA. 7 
2. OsTREA PRINCEPS, S. Wood. Tab. I, fig. 1, a—é, and Tab. II, fig. 2, a—é. 
P OstrEA unDULATA. Myst. Coq. Foss. de Belg., p. 324, pl. 24, fig. 7 a, and pl. 26, fig. 7 6, 
1844, (not J. Sowerby). 
Spec. Char. Testd magna, crassa, rotundatd ; valvd sinistrd converd, costatd, costis 
numerosis elevatis, radiantibus, divaricatis, concentricé undato-plicatis; valvd superiori pland, 
obsoleté costatd. 
Shell large, thick, and rounded; left or lower valve convex, ornamented with 
numerous, elevated, radiating and bifurcating coste, lines of growth or concentric 
laminze of an undulate or waving form, slightly reflected over the ribs; upper valve 
flat, with faint depressed, or nearly obsolete rays. 
Diameter, five inches. 
Locality, Cor. Crag, Sutton, Ramsholt, and Sudbourn. 
Red Crag, Sutton, Newbourn, and Bawdsey. 
This elegant shell was obtained by my friend, W. Whincopp, Esq., of Woodbridge, 
who has kindly permitted me to have it figured; a similar specimen, though not quite 
m so great perfection, is in the handsome museum recently erected by the liberal 
inhabitants of the town of Ipswich ; two or three more of the same dimensions are in 
the possession of E. Acton, Esq., of Grundisburgh, and these with another in the 
Cabinet of J. 8. Bowerbank, Esq., constitute the whole that I have seen of that 
magnitude. 
Such specimens appear to be very rare, as it was never my lot to find so large a 
one during my researches in the Crag of Suffolk, although the same shell, in its 
younger state (fig. 24), has been for many years in my cabinet, and from its presenting 
characters in that condition, by no means distinct, it was considered only as a variety 
of edulis, but the deeply sculptured markings, so well displayed in the specimen 
figured, seem to justify its being considered as a different species, although it 
must be confessed, the gradations of alteration between the young of this, and some 
of the varieties of the common edible species, are so trifling, that the line of 
separation cannot satisfactorily be pointed out. There are, in this genus particularly, 
perplexities in specific determination, so that no diagnosis can be given of any one 
species that is not liable to serious deviation, and the present name is assigned 
provisionally, from the apparently marked difference in the adult state, and which, if 
it be not specifically distinct, its elegance, a rather uncommon character in this genus, 
will entitle it to be ranked as a marked and peculiar variation, worthy of a dis- 
tinguishing appellation. 
A slightly sinuated form is visible on the posterior side, where the costz also 
appear more particularly to have a divaricating character. Upon the young shell the 
radiating ridges or coste are but few in number, and by no means prominent or 
distinct, appearing then strongly to resemble the edu/is ; as it enlarges, the differences 
become more visible, the rays being prominent and regular. The edge or inner margin 
of the shell is deeply indented with a slightly reflected edge, thus producing the sub- 
3 
