ORTMANN: FAMILIES AND GENERA OF NAJADES. 287 
Supra-anal and anal openings widely separated, the one about as 
long as the other, but the united part of the margin of the mantle 
Fic. 13. Anodonta cygnea (Linneus). Male, from Obra South Canal, Sepno, 
Prov. Posen, Germany. (Carn. Mus., No. 61, 4,956.) 
between them longer than either, with slight variations in length. 
Anal with crenulations, branchial with papillae. Palpi with the pos- 
terior margins united for one- 
fourth or one-third of their length. 
Gills and diaphragm as usual, inner 
lamina of inner gills free, except 
at anterior end. 
In the male, the septa of both 
gills are rather distant; in the sterile 
female the septa of the outer gill ie 
are very crowded, forming very 
narrow water-tubes (see Plate 
XVIII, fig. 7). The whole outer 
gill is marsupial, and at its edge 
there is heavy tissue which permits 
the distending of the gill when 
charged. Within the marsupium Fic. 13a. Left gills of a sterile 
female, from Mogelnitza River, Prov. 
each water-tube is divided, in the 
z 3 Posen, Germany. (Carn. Mus., No. 
breeding season, into three tubes, Yen 
61, 4,953-) 
two narrow lateral (secondary) 
water-tubes lying toward the faces of the gill, and a central larger 
