8 SYNOPSIS OF 



ensemble ne peut et ne doit former qu'un seul genre constituent a lui 

 seul la famille des Nayades."* 



It might be expected that some attempt of the application of M'Leay's 

 circular system should be made in regard to this family. Svvainson 

 says that "the progression of every natural series is in a circle. "f In 

 my attempts to verify this, I have not been successful. That the same 

 idea exists in the construction of species is evident through a great num- 

 ber, but that this idea is returned to the point at which it commenced 

 I am not prepared to admit. 



To form a systematic, and, so far as possible, a natural arrangement 

 of this family, has long occupied my serious attention. 



I was, from my first knowledge of the family, struck with the very 

 different aspect of the winged species, and, taking the hint of Lamarck,t 

 I thought that an important division could be made by separating the 

 connate from the free shells, and proposed the name of Symphynota 

 for such as were connate. I was not satisfied at that time in separating 

 a genus of this family by a character diflfering from that of the teeth, 

 but presumed that the family would be taken up by some one, if not 

 by myself, and that the first division of it would be symphynote and 

 non-symphynote Naiades. The numerous new species which have 

 been made known since, have satisfied me that this character cannot 

 be so extensively and usefully applied as I then thought it could, and 

 that it is not in fact free from the same objection which pervades so 

 many generic characters as adopted by the most intelligent naturalists, 

 viz. that perfect fading and mingling of character which interferes with 

 all the systems yet formed. 



* Vol. VI. p. 526. — I will be excused in taking this opportunity to correct an erroneous 

 impression on the mind of M. Deshayes. He says that I was not able to e.xaraine the collec- 

 tion of the Museum of Paris. " Malgre cette imperfection qu'il ne pouvait empecher, le travail 

 de M. Lea se reeommende a I'attention des naturalistes par ees observations judicieuses, des 

 descriptions exacles," etc. It would be strange, indeed, if after spending so many years in 

 the study of this family, that I should neglect, while in Paris, to see the collections from 

 which Lamarck made so many descriptions. I was frequently at the museum, and on one 

 particular occasion, by appointment of MM. Blainville and Ferussac, arranged, in the pre- 

 sence of these and other gentlemen, all the species of the Naiades that were in tiie museum, 

 and named them; and also presented to the museum about fifteen species which were new to 

 that great national institution. I also did the same thing for Baron Ferussac, having desig- 

 nated every specimen in his cabinet belonging to this family. 



t Swainson, in Lard. Cycl. Nat. Hist. p. 247. J "Vol. VL p. 76. 



