MYACID^. 13t 



Family MYACID^. 



Shell thick, strong and opaque ; left valve with a spatulate 

 cartilage-process, gaping posteriorly ; pallial line sinuated ; epi- 

 dermis wrinkled. Structure more or less distinctly cellular, 

 with dark nuclei near the outer surface ; cartilage-process com- 

 posed of radiated cells. 



Animal with the mantle almost entirely closed ; pedal aper- 

 ture and foot small; siphons united, partly or wholly retractile ; 

 branchiae two on each side, elongated. 



Mya, Linn., 1758. 



Etym. — My ax (-acis), a mussel (Pliny). Gaper. 



Distr. — 3 sp. Northern seas. Fossil, It sp. Pliocene — ; 

 United States, Britain, Sicil}^, 



Shell oblong, inequivalve, gaping at the ends ; left valve 

 smallest, with a large flattened cartilage-process ; pallial sinus 

 large. Most of the fossil " Myas " have an external ligament, 

 and are related either to Panopsea or Pholadomya. . 



Animal with a small straight linguiform foot ; siphons com- 

 bined, covered with epidermis, partially retractile; orifices 

 fringed, the branchial opening with an inner series of large 

 tentacular filaments ; gills not prolonged into the siphon ; palpi 

 elongated, free. 



The Myas frequent soft bottoms, especially the sandy and 

 gravelly mud of river-mouths ; they range from low-water to 25 

 fathoms, rarely to 100 or 145 fathoms. M. arenaria (cvi, 19, 20) 

 burrows a foot deep ; this species and M. truncata (cvi, 18) are 

 found throughout the northern and Arctic seas, from Ochotsk 

 and Sitka to the Russian Icy-sea, the Baltic, British coast and 

 northern United States ; in the Mediterranean they are only 

 found fossil. They are eaten in Zetland and North America, 

 and are excellent articles of food. In Greenland they are 

 sought after by the walrus, the Arctic fox, and birds. (0. 

 Fahricius.) 



Platyodon, Conrad, 1837. 



Distr. — P. cancellata, Conr. (cvi, 28). California. 



Shell ventricose, with concentric, undulating striae, and a small 

 groove from the apex to the ventral margin ; posterior side short, 

 radiately striated, spoon-shaped cardinal process dilated and 

 biemarginated. Siphonal orifices furnished with four valvular 

 testaceous appendages, which close them. 



TuGONiA, Gray, 1842. 

 Syn. — Le Tugon, Adanson. 



Distr. — 6 sp. West Coast of Africa. Fossil. Miocene ; Dax, 

 and the Morea. T.anatina, Gmel. (cvi, 21, 22). 

 10 



