406 NOTES ON FLORIDA UNIONID#—SIMPSON, 
Little is known regarding the variation and distribution of the mol- 
lusks of this region, as but a very small part of it has been explored. 
No doubt many allied forms, which from want of sufficient material I 
have not felt justified in reducing to synonymy, will have to be united 
when we have thoroughly worked up the mollusks of all the south- 
eastern States, and there are probably some valid species as yet unde- 
seribed. Perhaps my opportunities for studying the Unionidae: of ‘this 
region are as good as can be had at the present time. I resided four 
years in southwest Florida, and the collection I made at that time is 
very nearly complete as to species. IL have had for study all the mate- 
rial belonging to my friend the Rev. A. Dean, of Muncy, Pa.; the mag- 
nificent set of southeastern unios belonging to Mrs. George Andrews, 
of Knoxville, Tenn., including the shells collected by F. Rugel; the 
equally complete lot of material in the cabinet of Mr. William A. Marsh, 
of Aledo, I1l., who owns the finest private collection of these shells in 
existence, and who has greatly aided me in my work with numerous 
valuable notes and suggestions. In the National Museum I have had 
constant access to our general collection, most of which has been 
studied and named by Dr. Lewis and Mr. R. E. Call. This includes a 
large and nearly complete series of Mr. Wright’s new species, donated 
to the Museum by that gentleman. Besides this there is the unequaled 
collection of Dr. Lea, which includes most of the types from this region 
and a large ihc nen of valuable duplicates, as well as most of Dr. 
Gould’s species, which were sent by their author to Dr. Lea. 
A few words may not be out of place concerning the distribution of 
the Unionidae in the United States. There are two tolerably well de- 
fined areas of distribution in northern North America which contain 
very distinct assemblages of species, and each of these has a subregion 
peopled to some extent with different but allied forms. 
First. The Mississippi drainage area, embracing a territory of 1,250,000 
square miles. Within this region the Unionide attain a finer develop- 
ment than in any other part of the world, not only in the number of 
species, but in the magnificence of their forms andthe perfection of 
individual specimens. [tis here, where the streams flow over vast beds 
of limestone and where food is abundant, that the conditions for unio life 
are most favorable and nature has fairly reveled in the creation of the 
beautiful, the ponderous, and the grotesque. Here the genera Unio and 
Margaritana assume a variety of forms that are odd and strange; here 
are developed species with winged hinges, strong corrugations, knobs, 
and sinuses. 
South and west of this, in the streams running mostly through Texas 
and the eastern slope of Mexico into the Gulf, is found a small assem- 
blage of forms not met with in the Mississippi Valley, though closely 
related to the species found in that region. They have for the most 
part finely developed shells, and their relationship to those of the area 
just mentioned and the fact that many of the species of the great 
