502 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



he was led into several serious errors, his work has proved au imiiortant 

 aid in classification. 



H. and A. Adams followed with a classification in 1857, in which they 

 recognized the families Unionidi© and Mutelidte, dividing the former into 

 two subfamilies, Unioninee and Mycetopinse, and giving a list of the 

 then known species. 



Agassiz, in 1852, published a classification of the jSTorth American 

 Unionidee, based more especially on the anatomy, but much of his 

 work was hasty and careless, and as a result his groups are, for the 

 most part, heterogeneous assemblages of unrelated species. 



In 1893, von Iheriug published his Najaden von San Paulo, in which 

 he showed that while certain of the ]S^aiades began their existence on 

 hatching from the Qgg, as a glochidiwn, with a bivalve shell capable of 

 containing the soft parts, others developed into a lasidium, with three 

 segments, the middle one alone having a single shell. He showed that 

 the presence or absence of siphons by which the Mutelidie had been 

 separated from the Unionidte was not a constant character, even in indi- 

 vidual species, and ])laced the genera which he believed to have glo- 

 chidia in the family Unionidie, and those with lasidia in the Mntelida?. 

 I consider this tlie most important discovery that has yet been made in 

 the study of the ISTaiades. 



In 1896 the writer published a classification of the ifaiades, based 

 largely on his studies of shell characters. In that it was shown tliat 

 throughout one great group all the genera had shells with schizodont 

 hinge teeth or vestiges of theni, and in the rest, a smaller group, they 

 all had taxodont teeth, or vestiges of them. As all the genera whose 

 shells have schizodont teeth were believed by von Ihering to possess a 

 glochiclmm, and those with taxodont teeth have a lasidium, it seemed 

 as though there was a natural division of the Naiades into two families 

 Unionidse and Mutelidpe. 



Some years ago the Rev. and Mrs. L. T. Chamberlain, son-in-law and 

 daughter of Dr. Lea, suggested to Mr. Dall that a new edition of the 

 Synopsis, or if necessary a new work, should be prepared, and for this 

 purpose they generously ottered to contribute such sums as might be 

 needed for the iiurchase of material to add to the great collection left 

 by Dr. Lea to the IT. S. National Museum at his death, and for li: erature 

 that might be required in preparing the work. As the writer had made 

 a special study of the Naiades, the task of preparing the new Synopsis 

 fell to him. Since then Mrs. Chamberlain has been called away by 

 death, greatly regretted, but her husband has continued to cheerfully 

 furnish all the needed funds for carrying on the work to completion. 



While the labor of preparing the synopsis has been arduous, and 

 while it has been impossible to obtain material needed in many impor- 

 tant groups, or all the necessary literature, I feel that my opportuni- 

 ties for study have been exceptionally good. I have had constant 

 access to the great collection of Dr. Lea, the finest, no doubt, ever 



