PHOLAS. 113 



the front, where there is an upward curve to the posterior end, 

 which is broad and rounded, with sharp edges and a large 

 gape ; dorsal margins sloping almost equally on each side, the 

 posterior being the larger of the two : beaks placed at a dis- 

 tance of about fths from the anterior end : hinge-line flexuous : 

 hinge-plate extremely broad, folded over the umbonal area, 

 and adhering to the greater part of it ; it has no protuberance 

 or other process, and is consequently more or less worn away 

 in the centre by continual contact : apophyses curved, some- 

 what dilated, and concave at the points : dorsal shield trian- 

 gular, with the apex downwards and the sides turned in ; it 

 is almost rudimentary, and covers only the angle formed by 

 the meeting of the hinge-plate in each valve on the posterior 

 side ; the lines of growth are strong : inside marked with a 

 ridge, which corresponds to the outside furrow, and termi- 

 nates in a blunt tubercle : pallial scar narrow, very deeply 

 sinuated, and extending far within the shell : muscular scars 

 conspicuous ; posterior pear-shaped, lying near the edge of 

 the dorsal slope. L. 1*6. B. 2*8. 



Habitat : Mica-schist, coal-shale, Great Oolite, Ox- 

 ford clay, gypsum, and peat, on various parts of the 

 coast from Unst in Shetland (Edmondston and Dawson) 

 to Weymouth (Metcalfe), and throughout the greater 

 part of Ireland. Da Costa gives Cornwall also as a 

 locality. It is found in all our upper tertiaries from 

 the Belfast bed to the Coralline Crag, and especially in 

 boulder-clay and other deposits of the glacial period. 

 Uddevalla (Malm) ; Christiania, in newer deposits, 

 100 feet above the sea-level (Sars) ; Monteleone in 

 Calabria, as P. vibonensis (Philippi). Its extra- British 

 range in a recent state is chiefly northern. Iceland 

 (Mohr and Spengler); Scandinavia (Muller and others); 

 Heligoland (Frey and Leuckart) ; coasts of Holland 

 (Waardenburgh) ; north of France (De Gerville and 

 others) ; Charente-Inferieure (Aucapitaine) ; Marseilles 

 (Matheron, fide Philbert); it is also extensively distri- 

 buted in the New "World, e. g. Canada and the United 



