166 Fragments of Natural History. 
_— asperrimus of Lea. Unio crassidens of Lamarck. 
Kirtlandianus “ “ “ obliquus =“ 
“ coccineus -  Hildreth.| “ — verrucosus “ Barnes. 
“ phaseolus = “© melancorus “ Ra/finesque. 
“¢ crassus « Say. 
Besides the species which I have referred to, our western wa- 
ters abound with many others, which I have not examined with 
sufficient attention to allow me to decide with certainty whether 
their sexes are marked with a difference in the form of their shells, 
or whether they are exceptions to this rule. 
While making these examinations a few years since, I discov- 
ered in a number of instances a peculiar appendage to the young 
bivalves that I have not seen noticed by any author. : 
On raising these animals from their beds at the bottom of the 
streams, a small silky filament could frequently be seen issuing 
from between the valves of the shell, and on tracing it to its ori- 
gin, it was found to arise fromsthe margin of the animal immedi- 
ately behind the base of the muscular process, which is usually 
termed the foot. As the other extremity of this filament was ap- 
parently attached, in a few cases, to some portion of the animals 
of older individuals of the same species, or perhaps to the inner 
surface of their shells, I was led to conclude that there exists, for 
a certain period of time, a connection between the old and the 
young of the Naiades, analogous to the umbilical connection of 
the mammalia. In one instance I supposed that I had succeeded 
in tracing out a perfect connection of this kind between a young 
Unio crassus not half an inch in length, and a full grown speci- 
men. The filament that united them'appeared to pass to the anl- 
mals of both the old and young between the edges of the valves. 
On a stibsequent occasion, I saw a female U. cylindricus throw 
off the contents of her ovidust ; in jets, which I watched till they 
were dissolved and broken, so that each individual ovum was left 
to float in any direction the stream might force it. From this 
circumstance, it was evident that no umbilical attachment could 
be subsequently formed between the mother and her progeny, 
and therefore my conclusions must have been erroneous. 
The matter remained with me in this state of uncertainty until 
last. autumn, when the low stage of water and the eee’ 7 hot 
