108 PHOLADID^E. 



or slightly angular at the anterior end, exhibiting a long and 

 rather narrow gape towards the front, whence there is a re- 

 gular slope (less above than below) to the posterior end, 

 which is rounded and has a sharp edge, with a moderate gape ; 

 dorsal margin on the anterior side short, concave, and smooth: 

 beaks very near the anterior end: hinge-line flexuous: hinge- 

 plate extremely broad, and forming a single fold on the um- 

 bonal area, to which it adheres, the outer edge being free ; 

 the centre is marked across by a few indistinct furrows, re- 

 sembling the walls of the cells in P. dactylus, as sometimes 

 seen in that part of the shell ; and it is furnished with a 

 sharp ridge, that winds obliquely from above the apophysis 

 to the posterior side, and ends in a projecting spur- like pro- 

 cess ; this is more prominent in the right than left valve : 

 apophyses strong, narrow, curved, and concave at the point : 

 dorsal shield slightly bent, and shaped like a lance-head with 

 the point outwards ; it has a small boss near the broader end, 

 from which a shallow groove runs in the middle to the other 

 end, with a slope on each side ; the lines of growth are dis- 

 tant, diagonally arranged, and numerous. L. 1. B. 2-75. 



Var. subovata. Shell smaller, and somewhat oval, in con- 

 sequence of the posterior end being shortened or less de- 

 veloped. 



HABITAT : Coal-shale, Great Oolite, and Oxford 

 clay, chalk, marl, peat, submarine wood, and sand, from 

 Guernsey to Oban and the Moray Frith, as well as 

 throughout Ireland. Fossil at Belfast (Grainger, who 

 has recorded a specimen from that deposit measuring 

 3 inches by 1) ; Bracklesham (Dixon) ; Christiania 

 district in the newer beds, 100-120 feet above the 

 present level of the sea, and at Drontheim, 30-40 feet 

 (Sars). Abroad, it ranges from Iceland (Olafsen and 

 ~Povelsen,fide Miiller) and Norway (Loven) to the Black 

 Sea (Nordmann, fide" Middendorff) ; Sicily (Philippi) ; 

 and Algeria (Deshayes and others). 



Mr. Clark found it living in sand at Exmouth, and 

 M. Cailliaud in gneiss at Croisic. It occurs in com- 

 pany with P. dactylus and P. parva at Guernsey. This 



