88 GEORGE LEFEVRE AND WINTERTON C. CURTIS 
condition in the niarsupium throughout the winter, are not dis- 
charged until the following spring and summer. In fact, in some 
cases the close of one breeding period may overlap on the begin- 
ning of the next, as one may still find in late July a few straggling 
females gravid with glochidia formed in the previous autumn, 
while in other individuals of the species at the same time and in the 
same locality the eggs are passing into the gills for the next season. 
This seems to be true of several species of Lampsilis. We have 
encountered it in ligamentinus, Conner ('09) records it for radiatus 
and nasutus, while Ortmann ('09) states that his observations 
make it probable for ventricosus and luteolus. Yet, as Ortmann 
observes, it is generally true that an interval exists between the 
close of one period and the beginning of the next. This interval, 
however, varies in length with different species, in some extending 
from late spring until August, whereas in others it is of much 
shorter duration. It is also to be noted that the discharge of 
glochidia does not take place in all of the individuals of a species at 
the same time, but on the contrary spawning may extend over a 
considerable period throughout the spring and early summer (c/. 
Ortmann, I.e.). 
In the case of the summer breeders, the eggs are fertilized during 
late spring and summer, and spawning as a rule is over by the end 
of August. In the species belonging to this group of which we have 
the completest records, ovulation begins in May and early June 
and may continue throughout July, while after the end of August 
gravid females have not been found. 
In view of the above facts, it would seem to better accord with 
the actual conditions to separate the species with respect to the 
length of time that the glochidia remain in the marsupium, desig- 
nating them as those that have a ''short period" and those with 
a ''long period" of gravidity, rather than to distinguish them as 
"summer breeders" and "winter breeders," respectively, for 
with respect to the latter neither ovulation nor discharge of the 
glochidia takes place in winter. 
The breeding season is undoubtedly a generic character, for, so 
far as our observations have gone, all of the species belonging to a 
given genus have essentially the same period of gravidity. 
