232 DESCRIPTION OF 



"In column No. 1, no ova were found in the ovMucts of any of the enume- 

 rated species. They were carefully examined, as regards the oviducts, but as 

 to the ovaria, they were not, except in the single specimen of Unio JEsopus. If 

 the ovaria had been examined, no doubt the ova would have been found in 

 all of them, exclusive of sukatus, pileus and formosus. They were all taken 

 from September 19th, to November 13th, 1838. "^ 



"In column No. 2, many of the species contained in column No. 1, were 

 examined again in the Autumn of 1839, and found to have ova in the ovaria 

 and none in the oviducts. The others in column No. 1, that I had not an oppor- 

 tunity to examine would, I think, have been found in the same condition. In 

 this column it may be observed, that U. parvus and lachrymosus had ova in the 

 ovaria in March, also a single specimen of U. ruliginosus taken at Waynesville 

 in July. As this was not as advanced as six others taken at the same time, 

 their period is probably irregular. 



" Column No. 3, contains the species observed with the oviducts charged 

 with young in the Autumn of 1838 and '39. 



" Column No. 4, contains the species with oviducts charged with young at 

 various periods of 1840. — In columns No. 1, and 2, no ova were found in the 

 oviducts. 



" I have not been able to come to a satisfactory conclusion respecting the ges- 

 tation and period at which the Uniones discharge their young ; that it varies 

 between some groups of the species, I have no doubt. — For instance, take all 

 those in columns No. 1 and 2, which late in the Autumn have no ova trans- 

 ferred to the oviducts, while other groups, in columns No. 3 and 4, have the 

 oviducts charged with young at the same season. The latter probably dis- 

 charge in the Spring, or early Summer, and the former later. 



" In column No. 2, is a U. plicatus with ova in the ovarium in Autumn ; in 

 No. 4, is one with ova in the ducts in July. Suppose this to have discharged 

 in August, it makes a very long gestation. 



" In column No. 4, is a U. circulus, with ova in the oviducts, in March, and 

 another with ova in the oviducts, in July. The same species also in column 

 No. 3, with ova in the oviducts, in Autumn. From this I would infer that it 

 is irregular, or breeds more than once a year. In column No. 4, is a U. lute- 

 olus, with ova in the oviducts, in March, in August and in October. Some 

 that I observed in August had their hranchice so swollen, that they could not 

 shut the valves close. In this case the animal would have discharged in a 



