2 Trans. Acad. Sci. of St. Louis. 



has necessitated the reduction to synonymic rank of very 

 many forms it is only because the facts justify the reduction, 

 and the interests of sound scientific reasoning require it. Of 

 so much synonymy as grew out of personal differences between 

 former students it were better not to speak. It will always 

 stand as a reproach that the best interests of science have thus 

 suffered. 



Most of the opinions herein expressed, regarding the 

 specific value of very many forms, are based upon an exten- 

 sive private collection of Unionidce, which is geographically 

 and numerically all but complete. Added thereto are very 

 many facts gleaned during an engagement of some months 

 in the Smithsonian Institution, at Washington, the time of 

 which was largely devoted to the Unionidce, which had pre- 

 viously been studied by my old friend and preceptor, the 

 competent and painstaking Dr. James Lewis. Many facts, 

 chiefly, however, connected with geographical distribution, 

 were thus collated. 



A considerable number of American Unionidce, most of 

 which are represented in the fauna of Arkansas, were origi- 

 nally described by the great French naturalist, Lamarck. Con- 

 cerning these species there has been much difference of 

 opinion, and even yet, in certain cases, opinions are divergent. 

 To facilitate a correct understanding of Lamarck's species 

 his original descriptions are herein reproduced, and fuller and 

 more complete descriptions added, of forms which are believed 

 to be authentic. These descriptions are accompanied by 

 drawings in the several plates; some of these were executed 

 by the careful hand of Mr. Harry A. Pilsbry and are duly 

 accredited to him on the plates ; the remainder were drawn by 

 the writer. Added to the data thus assembled will be found, 

 for Lamarck's species, most of the synonyms which 

 have been erected as species upon his older described 

 forms. The determination of these synonyms was in 

 no sense a patriotic matter, but proceeded on the hard 

 lines recognized in science as just and right. The great 

 naturalist made serious errors, but these could not well be 

 avoided with scanty material and not too full locality refer- 

 ences. It is hoped that this rather full synonymy, — which is 



