pDabiane 
re | PROCEEDINGS OF THE NATIONAL MUSEUM. 421 
young or nearly adult fuscatus, and are generally sent out under the 
latter name, and for years I have been perplexed as to the two. This 
seems to be a somewhat rare shell, while the former is very abundant 
It is a rather wide thin species, slightly biangulate posteriorly, gener, 
ally light chestnut colored, slightly rayed, and having a pale chocolate . 
non-iridescent nacre. Old specimens sometimes become produced at 
the posterior ventral region until the outline of the shell is arcuate. 
Unio tortivus Lea. 
(Plate Lx1u, Fig. 8; Plate Lxiv, Figs. 1, 3, 4.) 
Unio tortivus Lea. Obs. 111, p. 42, Pl. x11, Oct. 2, 1840. Chattahoochee River, Georgia; 
Dr. Boykin. 
Unio tetricus Lea. (Plate Lx1v, Fig.2.) Obs. vit, p. 18, Pl. xx11, Fig. 78, June 23, 
1857. Flint River, near Albany, Ga.; Bishop Elliott. 
This small species is abundant in the Atlantic drainage of Georgia, 
extending into eastern Alabama, and throughout the greater part of 
the State of Florida. I found thousands of specimens in Horse Creek, 
Manatee County, of the latter State, in about latitude 27°. Itis as 
variable a species as U. Buckleyi; specimens often being found in 
Georgia greatly compressed, extremely wide and arcuate; or it may 
be oblong, oval, and considerably inflated.* The wide flat forms are 
exceedingly close to U. arctatus, or even U. Lazarus, and it is doubt- 
ful whether they are really distinct; while the more rounded specimens 
approach fuscatus and occultus. The adult shells of this species so far 
as I have seen are invariably dark; the epidermis ranging from chest- 
nut brown to black; sometimes feebly rayed when young; the nacre 
is chocolate or dark coppery, and usually dull. 
The species is better known as U. tetricus, but tortivus is the older 
name, and an examination of hundreds of specimens from Lea’s collec- 
tion and elsewhere convinces me that there is no dividing line between 
them. As a rule, tortivus is more compressed in general form, and 
tetricus more inclined to posterior biangulation, but this does not al- 
ways hold good. I have before me in one tray four specimens received 
from Mr. B. H. Wright (Museum No. 91134), collected in Lake Beres- 
ford, and labeled by him U. coruscus, which I have been much puzzled 
over. They are considerably inflated, wide, black, rather solid shells, 
with a single posterior ridge, slightly inclined to biangulation, and 
bluish chocolate nacre. In the lot sent to the Museum under the 
name of U. diasia, by Mr. Wright, from Lake Dias (Museum No. 91135), 
are five more, which are evidently the same. They seem to stand be- 
tween U. tortivus and the form which Mr. Marsh has named U,. Fer- 
rissti, and are, I think, a variety of the former. 
* Since the above was written the writer has received a very large and enormously 
swollen specimen of the above species, collected at Cowan Swamp, near St. Augus- 
tine, Fla., by Mr. Chas. W. Johnson, of the Wagner Institute, of Philadelphia, and 
of which two natural sized outlines are given. 
