958 The American Naturalist. [November, 
seen. These latter specimens are much thickened anteriorly 
are much inflated in that portion, but are compressed pos- 
teriorly. The male individuals are rather pointed behind, and 
the females are truncated. 
Unio elegans Lea. Caddo Lake, Cross Lake, Corney Bayou, 
and Bayou Pierre. Very scarce. 
Unio donaciformis Lea, in the larger Lakes and Bayou 
Pierre. Very scarce. 
Unio plicatus Lea. , Bayou Pierre. Mr. Williamson sent me 
the only specimens that seem to me undoubtedly this species. 
Unio perplicatus Con. Ouachita River, Bayou Pierre. 
Unio multiplicatus Lea. Caddo Lake, Cross Lake, Dorcheat 
Bayou, Bayou Pierre. The finest specimens were from Cross 
Lake, near Shreveport. These would rival some of the monsters 
from Spoon River, Ill., and seem entitled to the name heros. 
Unio undulatus Barnes, Bayou Pierre. Mr.Williamson has sent 
me some specimens that seem best placed under this species, 
though they could, without especial violence, be called multi- 
plicatus. 
Unio boykinianus ? Lea. Dorcheat Bayou. I collected one 
specimen that has been so identified by Mr. A. A. Hinckley. 
I have seen specimens of the species in the Philadelphia Acad- 
emy, and have looked up Lea’s figure, and think that my 
friend is about as nearly right as can be in some of these deli- 
cate matters. 
Unio trapezoides Lea, abundant in the larger lakes and bay- 
ous. I have also received specimens from the Ouachita River 
in Union Parish. In Caddo Lake this species is the most 
abundant. I collected many hundreds there. Some of the 
largest specimens, however, were from Cross Lake. This spe- 
cies seems to like the larger bodies of water where it has a con- 
siderable extent of rather level bottom of somewhat soft mud 
to dwell in. . The characters of this species are, in the main, 
rather constant. The amount of inflation varies a good deal, 
as also does the postero-basal angle in sharpness; and the pos- 
terior ridge from dorsal to basal margins varies in its acute- 
ness. There is a considerable variation in the distinctness of 
the folds, but the trapezoidal outline, the black epidermis, the 
