OF THE FAMILY OF NAIADES. 443 



Alasmodonta of Say, have been mentioned by two eminent 

 English conchologists, W. Swainson and G. B. Sowerby, as 

 well as in America by P. H. Nicklin. Mr Sowerby (Zool. 

 Journ. Vol. I. p. 55.) has rennited them under the name of 

 Unio^ of which he makes two great divisions : 1 . Without 

 teeth. 2. With teeth ; and these are each subdivided into 

 "winged" and "not winged;" which are again divided into 

 the various forms of teeth, or the "hinge line." The evident 

 objection to this arrangement is the difficulty of deciding 

 upon the passage from the " not winged" to the " winged." 

 Thus we do not find the Anodonta trapezialis and Jlnodonta 

 g-/aMca, which Lamarck describes as ^^ compresso-alatd," men- 

 tioned among the " winged," while we have " Jlnodon alatus 

 of Swainson and Lamarck," w^hich is not described in the 

 " Hist. Nat. des Animaux sans Vertebres*." 



It is evident that the apparatus for depositing the calca- 

 reous and epidermal matter on the elevated and connected 

 wing must be different from that of the inhabitant of free 

 valves, to w^hich it has been denied by nature. 



Lamarck and Barnes both mention in their description of 

 the U. idutus of Say, that M. Le Sueur thought this shell 

 should constitute a new genus. Since that time so many 

 connate shells have come to my notice, that I feel satisfied the 

 science of conchology will be subserved by the institution of 

 this natui'al genus, w^hich will embrace, in all probability, 

 several others, viz. Hyria of Lamarck, Dipsas of Leach, and 

 Cristaria. Prisodon, and Paxyodon of Schumacher, all of 

 which, Avhen they shall be found perfect, will most probably 

 turn out to be connate shells. Lamarck suspected his Hyria 

 to be connate, like the U. alatus; for w^hen describing that spe- 

 cies, he says, "Nos Hyries auraient-elles une pareille reunion 



and here must be considered as a species of Unio, and not a genus. The ob- 

 servant M. De Blainville has placed Castalia and Hyria among the Uniones, and 

 Iridina and Dipsas among the Anadontm. Castalia amhigua is undoubtedly a 

 fluviatile shell, and approaches most closely to the II. triangularis. The teeth 

 are those of the Unio, and it differs only in its longitudinal furrows from the gene- 

 ral characters of the Unio. 



* Say describes his An. gihbosa as being alated. 

 VOL. III. — 5 u 



