ANATOMY AND PHYSIOLOGY OF ANODONTA FLUVIATILIS. 173 
though of frequent occurrence, is always small, seldom or never exceed- 
ing three inches in length, thin and much eroded. All the species 
occurring at this locality, with the exception of A. fluviatilis, viz., A. 
implicata, U. complanatus, U. radiatus, U. ochraceous, U. cariosus 
and U. nasutws occur in much better condition than in any other 
locality in this part of the State. In a pond situated less than a mile 
from this locality, A. fluviatilis is found of unusually large size and 
but slightly eroded ; specimens five inches in length, with a height 
of three inches and a diameter of two and one-half inches are abundant, 
and some are found measuring more than six inches in length and 
three and one-half inches in height, as large and perfectly preserved 
Specimens as occur in any locality, while with the exception of this 
species there is not another shell, in the pond, either bivalve or 
univalve. In another locality a mile below Albany where Spherium 
rhomboideum is found in abundance and of unusually large size, 
Anodonta fluviatilis, though of frequent occurrence, is very small ; 
the largest specimen I have seen, among a collection numbering many 
hundreds, measures two inches in length. © 
A, fluviatilis thrives best in ponds, but is found in quite rapid 
streams, though even then the most favorable localities are in the 
comparatively quiet portion of the stream. 
The largest specimens I have seen, were found in the pond mentioned 
above, near the mouth of a sewer, where the mud was of a slimy char- 
acter and offensive to the smell. It is claimed that the male and 
female may be distinguished by the comparative diameter and gen- 
eral shape of the shell, but I have not been able to so distinguish 
them. In the fall of 1879 I collected about one hundred and fifty 
specimens of varying size—the shells were of different shapes and 
proportions, some quite flat, others extremely gibbous, the diameter 
sometimes being greater than the height. Among the first sixty I 
opened, there was not a single male, the outer gills of each specimen 
being filled with young. The remaining specimens were placed in a 
tank, and for several months undisturbed ; when I removed these ani- 
mals from the shells I found only four individuals without young in 
the outer gills, and as some of the animals had extruded a portion of 
the young from the gills, it is possible that the individuals above men- 
tioned may have had the young in the gill pouches earlier ‘in the sea 
son but had extruded them all. Though I am not prepared to say 
that the sexes are not distinct, the fact that nearly every specimen 
had young in the gills would seem to indicate that condition. 
When my attention was first called to it, it was too late to make any 
farther collections that season. The growth of an animal during a 
year, I have not been able to determine ; an individual which I have 
