ORTMANN: FAMILIES AND GENERA OF NAJADES. 243 
transverse direction), more independent structures, with an epithelium 
thrown up into folds. They are much closer together, and form much 
narrower water-tubes, which, when gravid, become ovisacs. There 
is no noticeable difference in the width of these water-tubes in the 
inner and outer gill. When charged, the ovisacs do not expand much, 
and their lumen remains subcylindrical, so that the whole marsupium 
does not swell to any considerable degree, and its edge does not dis- 
tend and remains sharp. 
The ova are red in color, and are lodged in the ovisacs in the shape 
of well developed placente (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, 1911b, pl. 89, fig. 2) are rather small, 
of suboval shape, without hooks. Length and height about equal, 
0.15 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 oftenred. Incertain 
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 papille of the anal and branchial openings, 
separation of anal and supra-anal, inner lamine 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 F. rubiginosa, a 
relationship, which has been assumed by others on the ground of the 
characters of the shell. 
