I.NTRODUOTIOIS 



8inco tlic publication of my fifth volume, when I thought that comparatively few forms of 

 the family Unioniilee remained unobserved, whether exotic or indigenous, there has been an 

 accession which could not have been imagined by the student of this branch of Zoology. In this 

 volume will be found a large number of very remarkable and fine species from Siam, the possession 

 of -which I owe to the kindness of W. A. Haines, Esq., of New York. It will be observed, that 

 while some of these have a resemblance to species in this country, they are in their character- 

 istics essentially Asiatic, and as we might expect, they are totally different from European forms. 



None of these being preserved, with their soft parts in alcohol, which is much to be regretted, 

 I am unable to say what difference might have been observed in that part of their economy. 

 They are not, however, likely to differ much, as their outer hard parts do not indicate any 

 peculiar differences in their anatomy from the general forms. 



The first part of this volume will be found to consist of exotic forms altogether, and perhaps the 

 most curious and interesting are the Plagiodon isocardioides, and Triquctra contorta. These 

 seem to be aberrant from the family type. 



The last half of this volume consists almost exclusively, (of part only,) of Uniones I have received 

 from Georgia, which State seems to be the Zoological centre of this form of life. There are inserted 

 here, thirty-eight new species from that State, and I have, I think, more than double that number 

 already described in the Proceedings of the Academy of Natui-al Sciences, or nearly ready to be given ; 

 and it must be remembered that the numerous streams of that State, and their tributaries in adjoin- 

 ing States, have not, perhaps, been one half explored by the detective eye of the Zoologist. The 

 greater part of those which I have in my possession, I owe to the great kindness of my friend, the 

 Right Rev. Stephen Elliott, of Savannah, whose ardent devotion to the study of this branch of 

 Natural History, has been crowned with such extraordinary developments. To him I owe the 

 advantage of examining and describing the soft parts of so many Georgian species, he having at 

 various times sent to me many hundi-eds of specimens in alcohol, and my kind friend promises me 

 that liis efforts shall not be diminished in these researches. I must also take the present oppor- 

 tunity gratefully to thank my other numerous friends, in Georgia and other States, for their con- 

 tributions, usually consisting of local species. Their names are recorded with each of the species 

 received from them. These, with those which have been before published as Georgian, number 

 about 120 species, and if we add those which have been described and known as coming from the 

 basin of the Tennessee River, will make about 150 species already known. That this nxnnber will 

 increase to over 200 species, I have no doubt. The peculiar topography of this State (Georgia,) 



