1893.] Mollusks of Louisiana. 945 
In the identification of my species I have to acknowledge 
gratefully the assistance of Messrs Wm. H. Dall, Chas. T. 
Simpson, Wm. A. Marsh A. A. Hinckley, R. E. Call, and Dr. 
V. Sterki. Either Mr. Simpson or Mr. Marsh, or both, have 
examined specimens of most of my Unionidz, and Dr. V. Sterki 
has examined nearly all of my Pupide. It has been my good 
fortune to examine a good many of Lea's and Conrad's types 
at the Smithsonian Institution and at Philadelphia Academy 
.of Natural Sciences, and I have been able to use the works 
found in the library of the Museum of Comparative Zoology at 
Harvard University, so that I think most, if not all, of the 
identifications are entirely trustworthy. 
To my friends who have aided me in collecting, and to those 
who have helped in the matter of identification, my sincere 
thanks are extended. To Dr. Otto Lerch, Geologist of Louisi- 
ana, my thanks are especially due for enabling me to do col- 
lecting throughout the summer. 
NOTES ON THE TOPOGRAPHY AND CLIMATE OF NORTHWEST 
LOUISIANA. 
In order that the physical surroundings of the mollusks 
herein noted may be better understood, it appears to be justifi- 
able that a few notes on the topography and climate of the 
section will be in place. 
Probably there is no portion of the United States so misun- 
derstood from a topographic standpoint as northwest Louisi- 
ana. Mostof the people who visit the state goto New Orleans, 
which stands from eleven to forty feet above the sea level, in 
almost the flattest portion of the inhabitable part of the State, 
and immediately jump to the conclusion that the whole State 
a jungle of swamps and alligators. It is undeniable that a large 
portion of the State stands very little above mean tide-water, 
and that swamps and alligators do abound, but the northwest- 
ern portion of Louisiana is moderately hilly. The mean level 
of the country, from Shreveport to Monroe, is about 400 feet 
above the sea level, the elevation reaching on the hills from 
150 to 300 feet higher. If one starts at Shrevesport, which is 
between 198 and 227 feet above the sea, and goes to Monroe, 
