Ortmann: Families and Genera of Najades. 243 



transverse direction), more independenl structures, with an epithelium 

 thrown up into folds. Thej are much closer together, and form much 

 narrower water-tubes, which, when gravid, become ovisacs. I 

 is no noticeable difference in the width of these water-tubes in the 

 inner and outer gill. When charged, the ovisacs do no1 expand much, 

 and their lumen remains subcylindrical, so thai the whole marsupium 

 does nol swell to am considerable degree, and its edge does not dis 

 tend and remains sharp. 



The ova arc red in color, and are lodged in the ovisacs in the shape 

 of well developed placentae (sticking together by their membranes). 

 The placenta-, conforming to the shape of the ovisacs, are subcylin- 

 drical, and are discharged whole through the anal opening. 



The glochidia (see Ortmann, [9116, pi. 89, tig. 2) are rather small, 

 of suboval shape, without hooks. Length and height about equal, 

 0. 1 5 mm. 



The color of the soft parts is somewhat variable, but generally 

 a yellowish-orange. The margin of the mantle, the distal part of the 

 foot, and the adductor muscles, are deeper in color (intense orange- 

 brown), while the gills are pale yellowish or brownish. The gills of 

 the gravid female appear red when charged with the ova, and inside 

 of the whitish abdominal sac the gonads are very often red. In certain 

 specimens the color of the soft parts is altogether paler, the bright 

 orange tints being missing, but this difference in color does not depend 

 on sex. 



Fusconaja cerina (Conrad). 



One male specimen at hand, received from L. S. Frierson. It is 

 from Bayou Pierre, De Soto Parish, Louisiana. 



Structure in all points like that of F. rubiginosa, and agreeing also 

 in minor details, such as the papilla? of the anal and branchial openings, 

 separation of anal and supra-anal, inner laminae of the inner gills, and 

 palpi. 



A female was not at hand. But Mr. Frierson writes to me con- 

 cerning this species: "eggs in four gills," and "cerina has the body 

 white in about half, but red in the other half of the specimens. Some 

 have red eggs. But red eggs and red body are not correlated." 



Thus it seems that this species stands very close to /•'. rubiginosa, a 

 relationship, which has been assumed by others on the ground of the 

 characters of the shell. 



