354 MYIDjE. 



Ochotsk, and North America, where they are employed as 

 articles of food. In the Vlatyodon of Conrad the valves 

 are cancellated, and the siphons are stated to bear at the ex- 

 tremity four testaceous, valvular appendages which close the 

 orifices of the tubes. 



Species of My a. 



arenaria, Linn. truncata, Linn. 



prsecisa, Gould. Uddevallensis, Forbes. 



Sub-gen. platyodon, Conrad. 



Shell ventricose, with undulated concentric strige, and a slight 

 furrow extending from the Leaks to the ventral margin ; pos- 

 terior side short, with radiating striae. Cardinal tooth erect* 

 dilated, bi-emarginate. 



cancellata, Conrad. 



Genus TUGONIA, Gray. 



Shell globular or sub-oval, very inequilateral, widely 

 gaping posteriorly ; beaks small, posteriorly reflexed. Hinge 

 with a small, rounded, concave, spoon-shaped process in each 

 valve, projecting obliquely in front, and joined to the valve ; 

 an approximated posterior denticle. Ligament external, elon- 

 gate, horny, marginal, placed transversely across the beaks ; 

 cartilage fixed in the spoon-shaped cavity. Muscular im- 

 pressions unequal, the anterior oval, on the cardinal margin 

 near the hinge ; the posterior small, orbicular, near the 

 denticle ; pallial impression very short and simply arched. 



Syn. Tugon, Adanson. 



Ex. T. anatina, Chemnitz, pi. 95, fig. 2, 2, a. 



In the genus Tugonia the cartilage-processes or spoon- 

 shaped teeth are similar in each valve, and the shell is 



