COKCSU'EllA. 



489 



S til- genus. N'ovaculma, Benson. N. gangetica, PI. XXII., 

 Fig. 10. >Sl7^eZ/ oblong, plain; epidermis thick and dull ; pallial 

 sinus rather small ; anterior pedal scar linear. I^istribution, 

 India, China. In the mud of river-estuaries. 



Family XYIII. — Mtacld^. 



Shell thick, strong and opaque ; gaping posteriorly ; pallial 

 Kne sinuated; epidermis wrinkled. Structure more or less 

 distinctly cellular, with dark nuclei near the outer surface ; 

 cartila,ge process composed 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. 



Fig. 365. 3Ij/a truncata, L, i. Brit, (after Forbes.) 



Mya, L, Gaper. 



Etymology^ my ax (-acis), a mussel. (Pliny.) 



Synonym, Platyodon, Conrad. 



Types, M. truncata, PL XXIII., Pig. 1. M. Arenaria, 

 Pig. 207, p. 396. 



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

 smallest, with a large flattened cartilage process ; pallial sinus 

 large. 



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. 



M. anatina, Chemn. (Tugonia, Gray), "West coast of Africa; 

 posterior side extremely truncated ; similar cartilage-processes 

 in each, valve. Fossil, Miocene ; Dax, and the Morea 



Distribution, 10 species. Northern Seas, West Africa, Philip- 

 pines, Australia, California, 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 



