-,0 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 jambonneau.x, 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, living often in sand or nmd, with their Ijeaks or pointed 

 extremity buried deep in the ground ; sometimes fi.\ed 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 tlie beak. 



The number of recent species is somewhat limited, although they have a very wide 

 geographical distribution, bemg 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 (?) Linnceus. Tab. VIII, fig. 11. 



Pinna pectinata. Linn. Syst. Nat., ed. 12, No. 264, p. 1 1(J0, 1767. 



— — Turt. Brit. Biv., p. 223, pi. 19, fig. 1, 1822. 



— — Forh. and Hani. Hist. Brit. iMoIl., vol. ii, p. 255, pi. 43, figs. 1,2, .ind 



pi. M, fig. S, 1849. 



— iNGENs. 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. ingcns, 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 



