XVI SYNOPSIS OF 



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 

 pi-rvadi's so many generic characters as adopted by the most intelligent naturalists, 

 viz., that perfect fading and mingling of character which interferes with all the sys- 

 tems 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 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 expect perfection, I believe, in any system. 



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

 Nayades to consist of one genus, Margaritifera, which genus he divides into the 

 following subgenera: 1. Anodonta; 2. Iridina; 3. Dipsas; 4. Triquetra; 1 5. Alas- 

 modonta; 6. Unio. 



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

 Families and a great number of genera, which do not seem to me to possess charac- 

 teristics sufficiently different to be adopted. They are as follows : 



Unio. Lam., represented by Unio sulcatus. Lea. 



Cunicula. Swain., " " Unio rubiyinosus. Lea. 



Ligumia. Swain., " Unio rectus. Lam. 



Theliderma. Swain., " Unio lacrymosits. Lea. 



Metjadomus. Swain., " " M. yigas. Swain. 



sEylia. Swain., " " Unio ovatus. Say. 



Naida. Swain., " " Unio ater. Lea. 



Cantliyria. Swain., " Unio spinosus. Lea. 



Mijsca. Turton, " Unio pictorum. Lam. 



Potomida. Swain., " " Unio sinuatus. Lam. 



Lymnadea. Swain., " " Unio alatus. Say. 



Iridea. Swain., " " Unio granosus. Lam. 



Castalia. Lam., " Castalia ambigua. Lam. 



Ndid. Swain., " Unio corrugatus. Lam. 



Hyria. Larn., " " Hyria syrmatophora. Lam. 



Hyridella. Swain , " " Unio aus trails. Larn. 



Iridina. Lam., " Iridina exotica. Lam. 



Calliscapha. Swain., " Iridina Nilotica. Sow. 



Afycetopus. D'Orb., " " Hycet. soleniformis. D'Orb. 



1 Klein. This, it would appear, Baron Ferussac intended should embrace my genus Symphynota, as 

 he included all he knew of them except S. bialata. 



