266 MYTILID^. 



adductor supported on a shelf within the beak ; pedal impres- 

 sion single, posterior. 



Animal with the mantle closed ; b^^ssal orifice small ; and 

 siphon very small, conical, plain, branchial prominent, fringed 

 inside; palpi small, triangular; foot-muscles short and thick, 

 close in front of the posterior adductor. 



D. polymorpha (cxxviii, 100; cxxix, 24) is a native of the 

 Aralo-Caspian rivers ; in 1824 it was observed by Mr. J. Sowerby 

 in the Surrey docks, to which it appears to have been brought 

 with foreign timber, in the holds of vessels. It has since spread 

 into the canals, docks, and rivers of many parts of England, 

 France and Belgium, and has been noticed in the iron water-pipes 

 of London, incrusted with a ferruginous deposit. 



MYTiLOPSis, Conrad, 1857. (Praxis, H. and A. Ad., 1857.) 

 Shell with a lamina on the hinge-shelf or septum. D. Sallei^ 

 Recluz (cxxix, 22). D. leucophaeata, Conrad. Brackish waters 

 of Chesapeake Bay, on oysters. 



DREissENOMYA, Fuchs. Septum transformed into a regular, 

 large, anterior muscular scar, pallial line with a deep posterior 

 sinus. D. Sch7'dckingeri^ Fuchs. Upper Tertiary ; Hungary. 



Septifer. Recluz, 1848. 



Distr. — Warm seas. Fossil ; Jurassic and Cretaceous. S. 

 Heberti, Desh. (cxxix, 23). 



Shell equivalve, very inequilateral; ventral margin subconcave 

 and cut out for the jjassage of the byssus ; beaks subterminal, 

 curved ; hinge without teeth, furnished with a lamellar septum ; 

 ligamental pits linear, marginal, dorsal, anterior, with a white, 

 nearly spongy margin within ; muscular impressions superficial, 

 the anterior small, rounded, the posterior large, subdorsal, 

 uniform. 



Animal marine, byssiferous. 



Myalina, Kouinck, 1842. 



Distr. — Fossil, 6 sp. Silur., Carb. — Permian; Europe. 31. 

 lamellona^ Koninck (cxxix, 25). 



Shell equivalve, mj'tiliform ; beaks nearlj^ terminal, septiferous 

 internally ; hinge-margin thickened, flat, with several longitu- 

 dinal cartilage-grooves ; muscular impressions two; pallial line 

 simple. The ligamental area resembles that of Area ohliquata^ 

 Chemn. 



Anthracoptera, Salter, 1863. 

 Syn. — Naiadites, Dawson, 1855 (part). 

 JEtym. — Anthrax^ coal, and pteron, a wing. 

 Didr. — Fossil, 10 sp. Carboniferous; Great Britain, West- 

 phalia, Nova Scotia, United States. 



