82 
IOWA ACADEMY OF SCIENCES 
undulata , and tappaniana, and Lampsilis nasutus and ockra- 
cens from Pennsylvania waters are included. Two of 
these examinations, as indicated in the accompanying 
tables, occurred in September. 
Table I. shows the distribution of the material exam- 
ined by species, sex, and time of observation. In addition 
to the fourteen hundred and ninety-emht included, thirty- 
one were excluded because the determination of sex was 
impossible through infestation of the sexual organs by 
parasitic cercaria to the utter atrophy of the germinal 
tissue. A single individual of Q. trigona was hermaphro- 
dite. 
Table II. exhibiting the findings, is largely self-explana- 
tory. The similarity of the closely related forms, in their 
time of maturity and method of carrying the young, is 
apparent. Because in certain species, the old glochidia 
are found still in the marsupium when examined in May, 
it is inferred that in these cases they have been carried 
through the preceding winter. 
Furthermore, though this is not shown in the tabula- 
tions, for the reason that in most species throughout the 
time of sexual maturity a sufficient number of both sexes 
are in a condition plainly unripe, and because of the 
absence of the glochidia and swollen gills containing 
them in certain females, when others of their species are 
normally gravid, it is believed that the period of sexual 
maturity does not always recur every year. 
