L7I BULLETIN NO. 23, UNITED STATES NATIONAL MUSEUM. 



laud moilusca of the United States, lie being' universally the acknowl- 

 edged authority on these families of moilusca. 



The most distinguished authors who have written on the subject of 

 the divisions of the Unionidw have acknowledged the difficulty of the 

 subject. The true definition of a species has much eugaged his atten- 

 tion, and he has in his synopsis endeavored to express his idea of what 

 constitutes a species in the following words : 



A species must be cousidered a j)riuiary established law, stamped with a persistent 

 form, a type, pertaiuing solely to itself, with the jiower of successfully reproduciug 

 the same form and none other. 



Dr. Lea has always held that the chief work of scientific societies is 

 in connection with their publications, because these reach all similar 

 bodies, and through them scientists, wherever science is cultivated. 

 The gathering of materials for a collection is necessary, although that 

 is of secondary importance. In regard to the date of papers, he always 

 considered that the day of readiug and presenting the communication 

 to a society, and depositing it, was the only reliable date, as from that 

 time the paper was ia the possession of the society and could not be 

 changed. 



This has been the usage with most of the learned societies of Europe, 

 although in this country some societies adopt the rule of issuing printed 

 descriptions as necessary to precedence. 



All Dr. Lea's papers, from first to last, were printed exactly as they 

 were read and presented to the Academy of Natural Sciences and the 

 American Philosphical Sociei. during a period of fifty-nine years, ex- 

 cept two specific names which had been used before. These he re- 

 quested permission of the society to change. 



The great use to men of science of the Smithsonian Institution is 

 universally acknowledged. It has been the medium of communication 

 between learned societies throughout the world, both in facilitating 

 correspondence aud interchanging publications. To Dr. Lea it has 

 been of great assistance from its establishment to the present time. 

 Its constant and safe conveyance of all his numerous memoirs, aud the 

 return of those of various authors by thousands, have been accom- 

 l^lished without a single loss. Thus the Zoological Society, of London, 

 has sent him all its Proceedings from 1831 ; the Asiatic Society of 

 Bengal since 1835; and the Imperial Eoyal Geological Society, Vienna, 

 from 1853. Professor Haidinger says in one of his letters : 



It is invaluable for that steady mutual intercouso for seieutilic purposes, in which 

 the Smithsonian, and in fact the United States, stands unrivaled. And Ihe most 

 friendly intercourse is certainly above all preferred by scientific investigators. 



Dr. Lea was accustomed to pass his summer, for many years, in Chester 

 County, so rich in its various minerals. In that and Delaware Couut^', 

 with his friends, Dr. Hartman, Mr. Jefleris, and Mr. Joseph Willcox, 

 many localities were searched, and some new ones discovered. Dr. Lea 

 found several new minerals which he called Cassinite, Patersonite, Leu- 



