490 MANUAL OF THE MOLLTJSCA. 



fatboms. M. arenaria burrows a foot deep ; this species ani M, 

 truncata are found througbout tbe nortbern and Arctic seas, 

 from Ocbotsk and Sitka to tbe Russian Ice-meer, tbe Baltic, 

 and Britisb coast ; in tbe Mediterranean tbey are only found 

 fossil. Tbey are eaten in Zetland and Nortb America, and are 

 excellent articles of food. In Greenland tbey are sougbt after 

 by tbe walrus, tbe Arctic fox, and birds. (0. Fabricius.) 



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

 Most of tbe fossil "Myas" bave an external ligament, and are 

 related citber to Panopcea or Pholadomya. 



CoRBTJLA, Bruguiere. 



Etymology, corhula, a little basket. 



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



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

 Turt. 



>S7/eZZ tbick, inequiyalve, gibbose, closed, produced posteriorly ; 

 rigbt valve witb a prominent tootb in front of tbe cartilage pit ; 

 left valve smaller, witb a projecting cartilage j)rocess ; pallial 

 sinus sligbt; pedal scars distinct from tbe adductor impressions. 



Animal witb very sbort, united sipbons; orifices fringed; 

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

 gills 2 on eacb side, obscurely striated. 



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

 Mediterranean, West Africa, Cbina. Inhabits sandy bottoms ; 

 lower laminarian zone — 80 fatboms. 



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

 India. 



Tbe external sbell-layer consists of fusiform cells ; tbe inner 

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

 it is very frequently detached in fossil specimens. Corbulomya, 

 Nyst ((7. complanata, Sby.), Crag., Britain. 



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

 Isle of Wight. Cartilage process broad and spatulate, received 

 between two obscure teeth in the rigbt valve. Tbe estuary 

 CorhulfB differ veiy little from tbe marine species. P. labiata 

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

 mud of tbe River Plata, but not above Buenos Ayres, and con- 

 sequently in water which is very little influenced by tbe 

 superficial ebb of the river. Tbe same species is found in banka 

 widely dispersed over tbe Pampas near San Pedro, and many 

 places in the Argentine Republic, five yards above the river 

 Parana. ( D arwin . ) 



SplieMia,TMri. S. Bingbami, PI. XXIII., Fig. 4. Shell 



