BIVALVIA. 31 
in the Sicilian Beds, I have not yet seen it from any of the three Crag Formations of 
Essex, Suffolk or Norfolk. As it is a fossil in the Clyde Beds, and may, probably, be 
hereafter found in the Crag, it ought not to be here passed over in silence. The 
specimen figured (which is the right valve) was given to me by James Smith, Esq., 
of Jordan Hill, and is undoubtedly identical with the British shell recently obtained in 
considerable plenty by Mr. George Barlee. 
Our specimen contains a good deal of animal matter, with some slight remains of 
colour, as indicative of its comparatively modern origin. The shell like that of 
P. tigerinus, is ornamented with curved radiating or diverging strie, but less promi- 
nent and distinct, and most visible at the lateral edges. A specimen of P. Dumasii, 
given to me by Professor Edward Forbes, which he obtained from a great depth in the 
Aigean Sea, does not appear to differ specifically from the British shell, and I have 
followed his example in uniting the two. Our fossil, however, appears to agree with 
the recent British specimens better than with the Dumasii from the Mediterranean, in 
having a rather larger posterior auricle; but my specimen from the Aigean differs also 
in that character from the Mediterranean shells, in having as large an auricle com- 
paratively as the British specimens. The number of ribs is a variable character ; 
sometimes the right valve has six, when the left one has only five, the depressions of the 
one valve corresponding to the elevations of the other, and vice versa. 
In this, as in most of the species of this genus, the auricles are comparatively 
larger in the younger shell than in the adult; my specimen, is a full grown shell, with 
six ribs or elevations, and the whole surface rayed or striated longitudinally, made 
rough or scabrous by elevated lines of growth, and the diverging or curved strie 
visible only at the sides.* 
7. PecrEN Princeps, J. Sowerby, Tab. VI, fig. 1. 
Pecren Princers. J. Sow. Min. Conch., t. 542, fig. 2, 1826. 
— — Woodward. Geol. of Norf., p. 44, 1833. 
a — S. Wood. Catalogue, 1840. 
_ — Morris. Cat. of Brit. Foss., p. 115, 1843. 
— Cutnronius? Say. Journ. Acad. Nat. Sci., vol. iv, p. 135, pl. ix, fig. 2, 1824. 
= — 2 Conrad. Foss. of the Med. Tert. of the United States, p. 47, pl. 23, 
fig. 1, 1838. 
—  svBLzviIGATUS? suv. Nyst. Coq. Foss. de Belge, p. 298, pl. 24, fig. 4, 1844. 
Spec. Char. Testa, orbiculari, subinequivalvi, convead, longitudinaliter eostatd, costis 
numerosis confertis, subsquamosis, interstitiis divaricatim striatis ; auriculis magnis sub- 
equalibus ; vaivd deatrd minore. 
Shell orbicular, slightly inequivalve, convex, externally ornamented with numerous 
close set, rounded and slightly squamose or imbricated striz, with a small inter- 
* A specimen much worn, and without its auricles, very recently found in the Red Crag, is in my 
Cabinet, and may possibly be of this species, but it is too much mutilated for fair examination. 
