956 The American Naturalist. [November, 
Unio camptodon Say, is found abundantly in the smaller 
streams throughout northwestern Louisiana. It seems to 
thrive best in small creeks and brooks that flow moderately 
rapidly, and have sandy bottoms. This species is so very 
abundant that, possibly excepting Unio texasensis, we are in- 
clined to call it the most abundant species. Itsrange of varia- 
tion is extremely great, and from the large suites that we ob- 
tained of it and the three following species, it seemed to us 
that we could trace their intergradation. 
Unio declivis Say. Corney and Cypress Bayous in Claiborne 
Parish, near Mt. Lebanon, and near Jonesville, Texas. Mr. 
Williamson sent me a specimen with pink nacre. 
Unio symmetricus Lea, in the creeks and bayous near Grand 
Cane. I havea good many specimens through the courtesy 
of Mr. Geo. Williamson, of Grand Cane. This species and 
jamesianus are, without doubt, synonyms, though a typical 
symmetricus can be distinguished from a typical jamesianus. I 
have seen Lea's types at the U. S. National Museum, and be- 
lieve these to be pretty typical. 
Unio jamesianus Lea, is abundant in the brooks and small 
creeks around Jonesville, and Port Caddoin Texas. Its habits 
closely resemble those of camptodon, with which its seems to 
connect by intermediate forms. 
Unio lachrymosus Lea, is one of the most abundant of the 
species found in thesection. Specimens were collected in Lake 
Bisteneau, Caddo and Cross Lakes, and in Bayous Dorcheat 
and Corney. The specimens are found in large numbers. The 
amount of variation is considerable, some specimens having a 
great number of pustules, while others have relatively few. 
Some specimens are much more compressed than others. The i 
largest and heaviest specimens were from Caddo Lake. 
Unio asper Lea, Corney Bayou, is found in other localities 
most likely ; shows some variation in the number of pustules. 
Unio pustulosus Lea, is not very abundant. Is found in most 
of the lakes and principal bayous. It is most abundant in 
Dorcheat Bayou. The specimens from this place are some- 
what more inflated than most of the specimens that I have 
seen from the more northern States. Some of the variations 
