60 MYIDiE. 



Family XX. MY'ID.E, (MYAD^) Fleming. 



Body oval : mantle rather thin, except at the edges : tubes 

 united, and wholly enclosed in a tough, leathery, brown sheath ; 

 orifices fringed : gills of moderate length, unequal on each side, 

 and striated : palps triangular, striated like the gills : foot 

 tongue-shaped, furnished with a byssal groove. 



Shell oval or oblong, somewhat inequivalve, usually gaping 

 at both ends, but more widely on the posterior side : epidermis 

 membranous : heahs more or less contiguous, not prominent, 

 turned towards the anterior side : cartilage internal, contained 

 between a perpendicular spoon-shaped and fixed receptacle, 

 lying under the beak in the right valve, and a canity of the 

 cardinal tooth or process in the left valve : hinge strong, fur- 

 nished with a small cardinal in the right valve, and with an 

 erect triangular tooth in the left valve, which latter tooth is 

 strengthened by an inside flange on the posterior side ; this 

 tooth is not inserted into the hinge of the right valve, but is 

 merely attached by the cartilage to the sunken receptacle 

 above mentioned: pallial scar broad and deeply sinuated : 

 muscular scars large and strongly impressed ; anterior elon- 

 gated, posterior triangular. 



The typical genus Mya is the only one that I con- 

 sider British. There seems to be no valid reason for 

 separating Sphenia (Turton) from it, either in respect 

 of the animal or of the shell. The so-called Panopea 

 Norvayica has a very different kind of hinge, besides 

 an external ligament : it belongs to Saxicava. So far 

 as is at present known, the Mya or " gaper " family is 

 restricted to the northern hemisphere. They inhabit 

 sand and mud, usually in the lowest part of the littoral 

 zone. 



Genus MYA^ Linne. PI. III. f. 1. 



The characters have been already given in the description 

 of the family. 



* So named from a supposition that it wa^; the juf^s of ancient writers. 



