xii SYNOPSISOF 



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

 should be made in regard to this family. Swainson says that " the progression of every 

 natural series is in a circle." 1 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 number, 

 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, 2 I thought that an important divi- 

 sion could be made by separating the connate from the free shells, and proposed the name 

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

 genus of this family by a character differing 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 exten- 

 sively 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 



Sowerby, after examining into the propriety of dividing the family into genera, came 

 to the conclusion of keeping but one genus, viz., Unio: this he divided into A without 

 teeth, B with teeth. These he subdivided into winged and not winged. Another sub- 

 division followed these, on the presence, form, and absence of teeth. There is evidently 

 much merit in this division, but it is not perfect; nor ought we to expect perfection, I 

 believe, in any system. 



Ferussac informed me, when in Paris, that he proposed to consider the Family Naiades 

 to consist of one genus, Margaritifera, which genus he divides into the following sub- 

 genera: 1. Anodonta; 2. Iridina; 3. Dipsas; 4. Triquetral 5. AJasmodonta ; 6. Unio. 



Swainson, in his Malacology, divides the Naiades of Lamarck into several sub-families 

 and a great number of genera, which do not seem to me to possess characteristics sufficiently 

 different to be adopted. They are as follows: — 



1 Swainson, in Lard. Cyd. Nat. Hist., p. 247. 



2 Vol. vi. p. 76. 



3 Klein. This, it would appear, Baron P. intended should embrace my genus Symphynota, as he included all 

 he knew of them except S. bialata. 



