THE NAIADES OF MISSOURI 321 
that of most Lampsilinae. The fact that the mature glochidia 
will not leave the conglutinated form after being extrued by the 
mother and because of the fact, too, that artificial infection of 
fish cannot be induced with its glochidia would lead to believe 
that its metamophosis may take place without parasitism. 
Genus Cyprogenia Agassiz. 
1852—Cyprogenia Agassiz, Arch. fur Naturg., p. 47; 1900b, Simpson, 
p. 609. 
(Type, Unto irroratus Lea.) 
ANIMAL CHARACTERS :—Branchial opening with short papillae; 
anal finely crenulate; supra-anal closely connected to anal; 
mantle edge antero-ventrad to branchial opening with fine crenu- 
lations for a short distance; inner laminae of inner gills free from 
visceral mass except at anterior end; palpi very small, pointed, 
very wide gap between them and anterior attachment of outer 
gills; marsupium consisting of 5-7 ovisacs anterior to center of 
outer gills, when gravid ovisacs immensely elongated and coiled 
post-dorsad; conglutinates white, very long and solid, subcylin- 
drical; glochidia semicircular, medium in size, ventral margin 
obliquely rounded, hinge line long and slightly upcurved. 
SHELL CHARACTERS:—Shell roundly triangular, subinflated; 
disk with peculiar nodulat structure; beaks more or less prominent, 
sculpture obscure; epidermis olive, painted with mottled rays; 
hinge complete; beak cavities rather deep. 
MISCELLANEOUS REMARKS:—The type of Cyprogenia, trrorata‘ 
(Lea), is not found in Missouri being entirely displaced by C. 
Aberti (Conrad). The variety of trrorata pusilla of Simpson, is so 
doubtfully reported for the St. Francis River that it is not listed 
here. Simpson is of the opinion that all C. ¢rrorata, reported for 
the localities west of the Mississippi, are really C. Abertiz. As to 
soft parts there is a similarity to those of Obliquaria; however, 
the slight differentiation of the mantle border antero-ventrad to 
branchial opening and also its uniquely coiled and extremely 
elongated ovisacs would rank it above. 
‘From Rafinesque’s evident description and figures (Ann. Gen. Sci. 
Brux., V, 1820, p. 312, pl. LX XXII, figs. 4, 5) we should make C-. trrorata 
(Lea) a synonym for C. stegaria (Raf.) 
