ORTMANN: FAMILIES AND GENERA OF NAJADES. 311 
narrower than the normal water-tubes, but have much heavier septa, 
with the usual marsupial structure of the epithelium. When charged 
the ovisacs swell so as to be considerably wider than the normal 
water-tubes. The marsupium protrudes beyond the original edge of 
the gill to a considerable degree, and the single ovisacs are subcylin- 
drical, and are somewhat curved backward. The ova and glochidia 
fill the ovisacs in the shape of rather solid placenta, and are packed 
close together through all of the placental mass (see Lefevre.and Curtis. 
1910, pl. 4, fig. 28). Probably the subcylindrical placente are dis- 
charged whole, although this has not been observed. The placentz 
can be taken out whole (see zbid., pl. 4, fig. 26), and in one of my 
specimens the holes through which placente had been recently dis- 
charged, have been seen (see Plate XVIII, fig. 10). The marsupium 
begins near the base of the gill, so that a considerable part of it is 
enclosed within the two original lamine of the gill. 
Lefevre and Curtis (1910, p. 97, fig. M) have figured the glochidium, 
and give its dimension as 0.225 X 0.23 mm. I find that this is sub- 
stantially correct. The glochidia are of medium size, almost sub- 
circular (their shape may be best compared with a circle a small 
section of which is cut off). Length and height about the same: 
0.22 mm. (see Plate XX, fig. 1). 
Color of soft parts whitish, with the edge of the mantle brownish, 
chiefly so in the region of the branchial and anal openings. Mar- 
supium white. 
There is much uncertainty as to the breeding season of this species. 
Lea (Obs., II], 1842) mentions ova as formed in the ovariumin autumn, 
and Sterki (1898, p. 20) found them in October. Lefevre and Curtis 
(1910, p. 89) place this species among the forms with a short breeding 
season, but without giving particulars. The sterile females collected 
by myself were all found in the month of September, at a time when 
most other bradytictic forms are gravid. The gravid females from 
Louisiana, collected by Frierson on August 6, were in part discharging, 
so that this would tend to show that the breeding season ends at that 
time. The statements made by Lea and Sterki might suggest that 
the breeding season begins rather late, in winter, and this assumption 
would agree with the facts at hand. Yet recorded observations are 
entirely too few, and attention should be directed to this question. 
The sterile specimen from Arkansas, collected in February, does not 
centribute to the solution of the question. 
