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 : heahs placed at a dis- 

 tance of about |ths from the anterior end : liinge-Une 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 : apojyliyses 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 : imllial scar narrow, verj^ 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-scliist^ coal-shale^ Great Oolite, Ox- 

 ford clay, orypsum^ 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 iu 

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

 range in a recent state is chiefly northern. Iceland 

 (Mohr and Spengler); Scandinavia (Miiller 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 



