528 



T. with a thin, brittle, flexuous (hell, of a whitifh 

 colour, tapering to the extremity: aperture orbicular; 

 infide fmooth, pervious: at the fmaller end the {hell be- 

 comes thick and flrong, and is furniflied within with 

 plates or lamina:, which contra6l that part very con- 

 fiderably, and leave a very fmall opening : the anterior 

 valves, attached to the head of the animal, are of a hemi- 

 fpheric form, one half the front projefting in a (harp 

 angle, and fomewhat pointed ; thin and brittle, finely, 

 and regularly ftriated longitudinally on the front angle, 

 which terminates in a regular line backward, where the 

 ftriac conform to the angular fliape of the valve, and run 

 tranfverfely acrofs the middle, or truncated part; this 

 part is covered with a light-brown epidermis; the hinder 

 part, or that which is attached to the animal, is white 

 and fmooth. 



The infide of each valve is white, furnilhed wdth a 

 long, flat, curved tooth, proje6iing inwards under the 

 hinge, as in mod the Pholades, and a fliort, lateral tooth 

 at the extremity of the hinge, coirefponding in each 

 valve: the margin, oppofue the hinge, runs to an acute 

 angle, at the point of which, in each valve, is a fmall 

 knob, which comes in contaft when the valves are 

 brought together; and as this is the only bearing point 

 befides the hinge, it may readily be conceived the fides 

 are extremely open. 



Near the extremity of the tail of the animal, are fixed 



two 



