40 CONCHOLOGY. 



FAMILY IV. 



Mr^RTA. Two genera. 

 1. Genus My a. PI. VI. 



Animal. Subcylindrical, enveloped in a mantle pierced only 

 with one interior and inferior hole for the passage of a very small 

 and conical foot ; the tubes very considerable, and completely 

 united ; a tolerably large mouth, oval, and with simple lips ; 

 very small labial appendages : branchial laminae inconsiderable ; 

 the external very short, the internal united with that of the oppo- 

 site side. 



Shell. Surrounded with a thick epidermis, which is prolonged 

 upon the tubes and the edges of the mantle of the animal ; tolera- 

 bly solid, with fine trenchant edges ; the summits very little 

 marked ; hinge dissimilar ; one or two oblique cardinal folds, di- 

 vergent, behind a horizontal spoon-shaped hollow upon the left 

 valve, corresponding with a hollow ; horizontal and cardinal in 

 the right valve ; two distinct muscular impressions. Inhabits the 

 British and American coasts. Eight species. 



Mya truncata. Mya erodona. 



M. arenaria. M. solenimyalis. 



M. hyalina.* M. acuta.* 



M. cancellata.* M. mercenaria.* 



2. Genus Anatina. PI. VI. 



Jlnimal. Unknown. 



Shell. Transverse, subequi valve, gaping at both valves, or in 

 one only ; no cardinal teeth ; one broad primary tooth in both 

 valves, projecting interiorly ; a lateral plate running obliquely 

 under the primary teeth. Sometimes there is a fissure extending 

 from the apex, giving the appearance of a second plate or rib. 

 Inhabits the British and American seas. Twelve species. 



Anatina iaterna. Anatina trapezoides. 



A. truncata. A. rugosa. 



A. subrostrata. A. imperfecta. 



