PANDORA. 25 



an erect cardinal, set at a right angle with the hinge-line, and 

 in the left valve a longer and somewhat horizontal cardinal, 

 set at an acute angle with the upper margin of the anterior 

 side ; the teeth and cartilage are on opposite sides of the beak, 

 and diverge from each other: inside highly polished and iri- 

 descent, slightly striated in a radiating direction ; edges thin 

 and sharp : scars more or less distinct, according to the thick- 

 ness of the nacreous lining. L. 0*6. B. 1*25. 



Tar. 1. tenuis. Shell much smaller, and of a delicate tex- 

 ture, proportionally broader or more produced at each end, with 

 an oblique and ilexuous outline ; dorsal margin straight. 



Yar. 2. obtusa. Shell smaller and thinner, longer in pro- 

 portion to its breadth; the posterior side larger, and not so 

 much produced or extended ; dorsal margin also straight. 



Monstr. Shell oval, with the sides shorter than usual ; 

 dorsal margin projecting a little outwards. 



Habitat : In sand, Channel Isles, at the recess of 

 spring tides, and in shallow water ; often among Zoster a 

 marina. Var. 1. Between 85 and 100 f. off Unst in 

 Shetland. Var. 2. From 7 to 50 f. on all our coasts. 

 The monstrosity is from the Hebrides and Shetland. 

 In a fossil state the typical form occurs in the Coralline 

 Crag, and the variety obtusa in the Red Crag ; both are 

 noticed by Philippi from different parts of the tertiary 

 formation in Sicily. The first has only a southern range, 

 from Guernsey to the iEgean ; while the distribution of 

 the other is wider, reaching to the Canaries in the 

 same direction, and extending northward to Spitzbergen. 

 In the iEgean, Forbes gave 4 f. for P. inaquivalvis, and 

 71-10 f. for P. obtusa ; and at Mogador M f Andrew 

 recorded the respective depths of 3 f. and 35-40 f. for 

 the two forms. The observations made by M. Martin 

 in the Gulf of Lyons showed similar results. 

 . The animal is shy and easily alarmed. Lacaze-Du- 

 thiers, in his valuable essay on the development of the 

 gills in LameUibranchiate Conchifera (Ann. Sc. Nat. 4 e 



vol. in. c 



