THE FAMILY OF NAIADES. 117 



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 subdi- 

 vided into winged and not winged. Another subdivision 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 ex- 

 pect 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 

 subgenera: 1. Anodonta; 2. Iridina; 3. Dipsas; 4. Triquetra;* 5. 

 Masmodonta-, 6. Unio. 



In Vol. 3 of our Trans, p. 398, Mr Nicklin expresses the opinion 

 "that the seven genera, now referred to the family of Naiades^ are 

 founded in artificial distinctions, and not in nature; and that in fact the 

 family contains but one genus." 



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 Platiris, and both of these into subgenera. 

 Under this system, the best place for the symphynote shells would be 

 a division of the subgenera into Symphynote and Non-Symphynote. 



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

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



VI. — 2 E 



