CONCHIFEIIA. 489 



Suh-genu3. Novaculina^ Benson. N. gangetica, PI. XXII., 

 Pig. 10. Shell oblong, plain; epidermis thick and dull ; pallial 

 sinus rather small ; anterior pedal scar linear. Distrihution^ 

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



PaMII^Y XYIII. — MYACIDyE. 



Shell thick, strong and opaque ; gaping posteriorly ; pallial 

 line sinuated ; epidermis wrinkled. Structure more or lesa 

 distinctly cellular, with dark nuclei near the outer surface; 

 cartilage process composed of radiated cells. 



Animal with the mantle almost entirely closed ; pedal aper- 

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

 Lranchise two on each side, elongated. 



Fig. 265. Mya truncata, L. i-. Brit, (after Forbes.) 



Mya, L. Gaper. 



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



Synonym, Platj^odon, Conrad. 



Tyjyesy M. truncata, PI. XXIII. , Pig. 1. M. Arenaria^ 

 Fig. 207, p. 396. 



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

 smallest, with a large flattened cartilage process ; pallial sinus 

 large. 



J. //tmaZ 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. 



2[. 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, AVest 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 Hii 



y3 



