REPRODUCTION IN THE UNIONID^E 
89 
Although our records in detail for each species will be published 
in our forthcoming report to the Bureau of Fisheries, the follow- 
ing lists show the distribution, with respect to the long and the 
short breeding seasons, of the genera which have come under our 
observation. 
Long period of gravidity. — Alasmidonta truncata; Anodonta 
cataracta, grandis, implicata; Arcidens confragosus; Lampsilis 
(Proptera) alatus, anodontoides, gracilis, higginsii, laevissimus, 
ligamentinus, luteolus, rectus, subrostratus ventricosus; Obo- 
varia ellipsis; Plagiola elegans, securis; Strophitus edentulus; 
Symphynota complanata, costata. 
Short period of gravidity. — Obliquaria reflexa; Pleurobema 
sesopus; Quadrula evena, heros, lachrymosa, metanevra, obliqua, 
plicata, pustulosa, trigona, undulata; Tritogonia tuberculata; 
Unio complanatus, gibbosus. 
Ortmann ('09) has recently published some observations on the 
breeding seasons of the Unionidae of Pennsylvania, supplemented 
by data from Lea and Sterki, and although he merely records a 
species as gravid or not in a given month, his results in all essential 
points agree closely with ours. He includes among ''winter 
breeders" several genera which we have not had under observa- 
tion, namely, Truncilla, Micromya, Cryprogenia, Ptychobranchus 
and Anodontoides, while Arcidens and Obliquaria, which we have 
recorded, do not appear in his lists of ^Svinter breeders" and '^sum- 
mer breeders," respectively. Although in many cases we have 
had the same species under observation, his records include a num- 
ber that are absent from ours, while our list supplements his espe- 
cially by the addition of several species of Quadrula, for which 
data have previously been quite meagre. 
By examining the two sets of observations, it will be found that, 
whereas the Homogense and Mesogense are represented in both 
groups, some genera in each having the long period and others the 
short period of gravidity, the Heterogense, Ptychogenae, and Dia- 
gense are so-called ^'winter breeders" exclusively, while the Tetra- 
gense breed only in the summer. 
The breeding seasons, as defined above, are based upon data col- 
