50 MOLLUSCA FROM THE CRAG. 
cirrhi or fringes round their posterior part; and a single row upon the anterior ; 
foot somewhat small and slender, furnished with a byssal groove; no projecting 
siphonal tubes. 
Animals composing this genus have their valves particularly thin, considering 
their dimensions, which sometimes attain considerable magnitude. In the recent state 
they are generally of a brownish or horny colour, which with their angular form have 
obtained for them, in France, the vulgar name of jambonneaux, or little hams. The 
shell gapes slightly at the anterior part near the beaks, through which is protruded a 
set of fibrous threads or byssus, so long as to have been occasionally manufactured 
into gloves and stockings. They are exclusively marine, having a range in depth 
somewhat considerable, livg often in sand or mud, with their beaks or pointed 
extremity buried deep in the ground; sometimes fixed to submarine bodies, by means 
of the byssus, which it is said to be capable of displacing at will by the aid of its foot. 
The two valves are closely united or soldered, as it were, together, along the dorsal 
edge, and are incapable of much expansion, but they gape widely at their larger or 
posterior extremity, opposite the beak. 
The number of recent species is somewhat limited, although they have a very wide 
geographical distribution, being found in most parts of the world, and the fossil species 
date as far back in time as the Oolitic Period, from which Formation there is one 
strongly resembling an existing form. 
1. PINNA PECTINATA (?) Zenneus. Tab. VIII, fig. 11. 
Pinna pectinata. inn. Syst. Nat., ed. 12, No. 264, p. 1160, 1767. 
— — Turt. Brit. Biv., p. 223, pl. 19, fig. 1, 1822. 
— — Forb. and Hanl. Hist. Brit. Moll., vol. ii, p. 255, pl. 43, figs. 1, 2, and 
pl. 53, fig. 8, 1849. 
— «ncens. Mont. Test. Brit., pp. 180, 583, and Sup., p. 72. 
— — S. Wood. Catalogue, 1840. 
A few fragments or imperfect specimens of a species of this genus have been 
obtained by myself from several localities in the Coralline Crag, but they are not in 
sufficiently good condition for instituting a fair comparison; what there is of them 
seem to present recognisable characters, and to correspond with those of the above- 
named recent species, and may, at least for the present, be considered as identical. 
In my Catalogue it was placed under the name of P. ¢zgens, Mont., which the authors 
of the ‘ Hist. of Brit. Moll.’ have determined to be only a variety of pectinata ; the 
spiny or scaly sculpture of that shell being generally removed by abrasion as it 
advances in age. 
In the small portion of what remains of our fossil, the radiating lines cover about 
half the shell, or from the dorsal edge extending into the middle of the valve; the 
ventral portion being sinuated and much thickened at the edge where the presumed 
byssus protruded, and the exterior is on. that side ornamented with subconcentric or 
