THE FAMILY NAIADES, 5 



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 vf\i\\ teeth. These he subdivided into winged and not 

 winged. Another subdivision followed these, on the pre- 

 sence, 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 in- 

 formed me when in Paris that he proposed to consider the 

 Family Naiades to consist of one genus, Margatifera, which 

 genus he divides into the following subgenera: 1. Jinodonta, 

 2. Iridina ; 3. Dipsas ; 4. Triquetra;* 5. Masmodonta; 

 6. Unio. 



After mature reflection, I have come to the conclusion, in 

 forming this systematic arrangement and catalogue, to divide 

 the family into two genera, Margarita and Iridina, and the 

 first into subgenera. In the fact, as we are informed by M. 

 Deshayes, that Iridina possesses tubes, I think, although the 

 form of the dorsal margin of the valves is without teeth, as 

 in the Anodontu, it must be considered a distinct genus from 

 Unio, which we must recollect like Anodonta, &c. forms 

 two temporary tubes with the posterior edge of the mantle 

 which is fringed with cilia or palpi, serving to determine the 

 direction of the jet of water which flows in a constant stream 

 through the superior temporary tube. Under this system, the 



* Klein. This it would appear Baron F. intended should embrace my genus 

 Symfihijnota, as he included all he knew of them except S. hialata. 



