230 DESCRIPTION OF 



Continuation of Mr. LeoHs Paper on Fresh Water and Land Shells. 

 Read February I9th, 1841. 



In a paper read before the Society July 15th, 1837, 1 gave the result of some 

 observations made in regard to the anatomy, gestation and geographical distri- 

 bution of the family Naiades, and I mentioned at the time that it was my inten- 

 tion to pursue the subject. Circumstances, however, have prevented my 

 undertaking the thorough examination of the habits of the species and their 

 structure, which I intended. At my request, however, my brother T. G. Lea 

 has made some valuable observations during the last three years at Cincinnati, 

 where these shells are numerous, and the size often large. A digest of these 

 observations has been made by him, and the result, though not entirely satis- 

 factory, will make some advance towards a knowledge of the periods of some 

 of the species. 



Sexual difference is no longer a matter of doubt,* but the period and mode 

 of impregnation^ as well as the length of gestation and the time oi parturition, 

 are either unknown or but partially understood. 



At page 52, Vol. 6, of the Transactions, I mentioned having seen in a single 

 instance the ejectment of a number of sacciform oviducts in quite a rapid 

 succession from the Unio complanatus. Dr. Kirtland has since, as he informs 

 me by letter, " twice seen the females of Unio cylindricus throw off their ova 

 per saltum, or with a kind of jet. The portions discharged were collections of 

 a vast number of individuals, aggregated in oblong masses, conforming with 

 the shape of the cells of the ovarium. Soon after they were discharged, they 

 appeared to crumble to pieces, and the several individuals fell down among 

 the sand." 



These observations corroborate mine; and we may conclude that we have 

 one fact established in two species in regard to parturition. 



The Anodonta, so far as I have been able to observe them, are ovoviviparous, 

 but, whether they, as some species of the Uniones do, attach themselves when 

 young by a byssus, I have not had the means to determine. In Silliman's 

 Journal for July, 1840, Dr. Kirtland published an interesting account of this 



* Transactions, vol. vi. page 49. 



