490 ^ MAJflTAL OF THE MOLLttSCA. 



fathoms* M. arenaria burrows a foot deep ; this species and M. 

 truncata are found throughout the northern and Arctic seas^ 

 from Ochotsk and Sitka to the Eussian Ice-meer, the Baltic, 

 and British coast ; 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.) 



Fossil, 17 species. Pliocene — . United States, Britain, Sicily. 

 Most of the fossil "Myas" have an external ligament, and are 

 related either to Pano^pcBci or Fholadomya. 



CoRETJLA, Bruguiere. 



Etymology, corbula^ a little basket. 



Type, C. sulcata, PI. XXIII., Pig. 2. 



Synonyms, Erodona, Daud. (.=Pacyodon, Beck.) Agina, 

 Turt. 



Shell thick, inequiyalve, gibbose, closed, produced posteriorly ; 

 right valve with a prominent tooth in front of the cartilage pit ; 

 left valve smaller, with a projecting cartilage process ; pallial 

 sinus slight; pedal scars distinct from the adductor impressions. 



Animal with very short, united siphons; orifices fringed; 

 anal valve tubular ; foot thick and pointed ; palpi moderate ; 

 gills 2 on each side, obscurely striated. 



Distribution, 66 species. United States, Norway, Britain, 

 Mediterranean, West Africa, China. Inhabits sandy bottoms ; 

 lower laminarian zone — 80 fathoms. 



Fossil, 120 species. Inferior Oolite—. United States, Europe, 

 India. 



The external shell-layer consists of fusiform cells ; the inner 

 is homogeneous and adheres so slightly to the outer layer, that 

 it is very frequently detached in fossil specimens. Corbulomya, 

 Nyst [C. complanata, Sby.), Crag., Britain. 



Sub-genera, Potamomya, J. Sowerby. P. gregaria. Eocene, 

 Isle of Wight. Cartilage process broad and spatulate, received 

 between two obscure teeth in the right valve. The estuary 

 Gorbulce differ very little from the marine species. P. labiata 

 (Azara, D'Orbigny), PL XXIII. , Fig. 3, lives buried in the 

 mud of the Eiver Plata, but not above Buenos Ayres, and con- 

 sequently in water which is very little influenced by the 

 superficial ebb of the river. The same species is found in banks- 

 widely dispersed over the Pampas near San Pedro, and many' 

 places in the Argentine Eepublic, five yards above the riveit 

 Parana. (Darwin.) 



Sjilieuia, Turt. S. Binghami, PI. XXIII. , Fig. 4. Shelt 



