166 



Fragments of Natural History. 



Unio asperrimiis of Lea. 



" Kirtlandianus " " 

 -'■' coccineus " Hildreth. 



" phaseolns " " 



" crassus " Say. 



Unio crassidens of Lamarck. 

 " obliquus " '• 

 " verrucosus " Barnes. 

 " melancorus " Rajinesque. 



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 from the 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 ani- 

 mals of both the old and young between the edges of the valves. 



On a subsequent occasion, I saw a female U. cylindricus throw 

 off the contents of her oviduct 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 protracted hot 

 weather, enabled me to pursue my researches more extensively 

 and with better success than on former occasions. 



