CONCHIFERA. 275 



Cast ALIA, Lamarck. 



Type, C. ambigua, PI. XVIII. fig. 4. Syn. TetraplodoD, Spix. 



Shell ventricose; trigonal; umbones promiaent, furrowed; hinge-teeth 

 striated; anterior 2.1, short; posterior 1.2, elongated. 



Animal with mantle-lobes united behind, forming two distinct siphonal 

 orifices, the branchial cirrated. 



Distr. Rivers of S. America, Guiana, Brazil. 



AxoDON, Cuvier. Swan-mussel. 



Tyipe, A, cygneus, fig. 171. p. 245. Etym. Anodonios, edentulous. 



Shell like unio, but edentulous ; oval, smooth, rather thin, compressed 

 when young, becoming ventricose Avith age. 



Animal like unio : the outer gills of a female have been computed to 

 contain 600,000 young shells {Lea). See p. 19. 



Distr. 50 sp. N. America, Europe, Siberia. Fossil, 5 sp. Eocene — .Europe. 



M. D'Orbigny relates that he found great quantities of small Anodons 

 {ByssO'anodontaParaniensis,D'Ov\).) 4 lines in length, attached by a byssus, 

 in the R. Parana, above Corrientes. 



Iridina, Lamarck. 



Syn. Mutela, Scop. Spatha, Lea (including Mycetopus). 



Type. I. exotica, PL XYIII. fig. 5. Etym. Iri^, the rainbow. 



Shell oblong ; umbones depressed ; hinge-line long, straight, attenuated 

 towards the umbones, crenated by numerous unequal teeth ; ligament long 

 and narrow. 



Animal with mantle-lobes united posteriorly, forming two short siphons ; 

 mouth and lips small ; palpi immense, oval ; gills united to the body. 



Iridlna ovata (Pleiodon, Conrad), has a broader hinge-line. 



Distr. 6 sp. Rivers of Africa, Nile, Senegal. 

 Mycetopus, D'Orbigny. 



Etym. Mzikes a mushroom, pons the foot. 



Type, M. soleniformis, PL XVIII. fig. 6. 



iS/i^// elongated, sub -cylindrical, gaping in front; margins sub -parallel, 

 hinge edentulous. 



Animal with an elongated, cylindrical foot, expanded into a disk at the 

 end ; mantle open ; gills equal ; palpi short. 



Distr. 3 sp. R. Parana, Corrientes ; R. Amazon, Bolivia. 

 yETHEUiA, Lamarck. 



Type, E.. semilunata, PL XVIII. fig. 7. {aitherios, aerial.) 



Shell irregular, inequivalve ; attached by the umbo, and tubular processes 

 of one of the valves, usually the left ; epidermis thick, olive ; interior pearly, 

 blistered (as if with air-bubbles) ; hinge edentulous ; ligament external, with 

 a conspicuous area and groove in the fixed valve ; two adductor impressions, 

 the anterior very long and irregular ; pallial line simple. 



