242 IRIDINID^. 



Anodonta, Cuvier. 



Etym. — Anodontos, edentulous. Swan-mussel. 



Syn. — Limnseoderma, Poli, 1835. Hemiodon, Swains., 1840. 



Distr. — 200 sp. World-wide. Fossil. Laramie Gr. — ; N. Am, 

 A. cygnea, Linn, (cxxiv, 96). 



Shell like Unio externally, usually much thinner and smooth ; 

 hinge without teeth. 



Dr. Lea divides the species as he does Unio. 



The following subgeneric groups are without much value : 



LAMPROSCAPHA, Swaiuson, 1840. Shell transversely elongated, 

 narrow ; beaks subanterior A. ensiformis, Spix. 



PATULARiA, Swainson, 1840. (Glabaris, Gray.) Shell cordiform 

 or rounded. A. latomarginata, Lea (cxxiv, 94), 



GONIDEA, Conrad, 185T. Shell wedge-shaped, posterior slope 

 defined by a high angle ; a rudimentary cardinal tooth in the 

 right valve fits into a depression in the left valve. A. angiclata. 

 Lea (cxxiv, 95). 



?AMN1GENIA, Hall, 1883. Like Anodonta in form and external 

 characters ;. probably fresh-water or estuary. A. Gatskillensis, 

 Yanuxem. Fossil; Oneonta sandstone, N. Y. 



Family IRIDINID^. 



Shell externally like Unio ; hinge-line usually crenated, making 

 numerous transverse teeth, or with lamellar teeth more or less 

 crenated. 



Mouth and lips small, labial palps very large, oval, attached 

 by their straight edges, without any free points as in Unionidse. 

 Mantle-lobes united posteriorly, and prolonged into two short, 

 unequal siphonal tubes ; gills large, nearly equal, united to the 

 body. Foot large, thick, compressed, tongue-shaped, angular in 

 front. 



Iridina, Lamarck, 1819. 



Etym. — Iris, the rainbow. 

 ' Syn. — Mutela, Scop., 1177. Platiris, Lea. 



Distr. — 9 sp. Rivers of Africa, Nile, Senegal. I. exotica, TtSim. 

 (cxxiv, 99). 



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. 



CALLiscAPHA, Swaius., 1840. Hinge crenated near the umbones 

 only. /. Nilotica, Lam. 



PLEiODON, Conrad, 1885. Cardinal margin wide, profoundly 

 crenulated. I. ovata, Swainson (cxxiv, 100). 



