949, IRIDINIDA. 
Awnoponta, Cuvier. 
Etym.—Anodontos, edentulous. Swan-mussel. 
Syn.—Limneoderma, Poli, 1835. Hemiodon, Swains., 1840. 
Distr.—200 sp. World-wide. Fossil. Laramie Gr.—; N. Am, 
A, cygnea, Linn. (cexxiv, 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, Swainson, 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, 1857. 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. angulata, 
Lea (cxxiv, 95). 
? AMNIGENTA, Hall, 1883. Like Anodonta in form and external 
characters; probably fresh-water or estuary. A. Catskillensis, 
oa 
. 
Vanuxem. Fossil; Oneonta sandstone, N. Y 
Famity IRIDINID2®. 
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 Unionide. 
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. 
Iripina, Lamarck, 1819. 
Etym.—Iris, the rainbow. 
Syn.—Mutela, Scop., 1777. Platiris, Lea. 
Distr.—9 sp. Rivers of Africa, Nile, Senegal. J. exotica, Lam. 
(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, Swains., 1840. Hinge crenated near the umbones 
only. J. Nilotica, Lam. 
PLEIODON, Conrad, 1835. Cardinal margin wide, profoundly 
crenulated. J. ovata, Swainson (cxxiv, 100). 
