Sowerby on the Lamarckiari Naiades. 55 



and Hyria: -with two wings and a lamelliform tooth on each side 

 the umbo, (Dipsas of Leach) between Anodon and Hyria : and 

 with lateral teeth and rather elongated cardinal teeth, (Caslalia 

 ambiguct) Lam.) between Unio and Hyria. The same shades of 

 difference occur also in the forms of the shells as well as in their 

 thickness ; but in these respects, as well as in the thickness 

 of their hinge teeth, each species appears to be subject to 

 very great variation, for which reason we shall not enter further 

 into particulars. Moreover, we think we have already said 

 enough to prove that unless it be thought wise to elevate each of 

 the peculiar sorts we have mentioned, and many more, into distinct 

 genera, it will be positively necessary to unite them altogether 

 under one generic appellation : we propose Unio as equally appli- 

 cable to all ; and we here annex a tabular view of the divisions of 

 the genus as far as our observations have pointed them out ; further 

 divisions may probably be found useful in arranging the species, 

 which may arise out of the oblique or straight position of the hinge 

 teeth : and such other characters as are not subject to variation or 

 purely specific. 



UNIO. 



f hinge line simple Anodontes, Lam, 



I slightly crenulated> T ., „., .. ~ 



not I "atthe umbones \ Ind> Nllot '«>, Sow. 



winged J crenulated Iridinae species, 



undulated 5 A T nodon rugosus, Sw. 



I. ^Unio anodontina. Lam. 



wm „ e( l <Anodon alatus, Sw. & Lam, 



I A. crassus, Sw. 

 f lamelliform lateral teeth only. Dipsas, 

 winced J' ame Uif orm cardinal and lateral teeth. Hyria*. 

 ° J lamelliform lateral and short cardinal 



C teetn Unio alatus, Sw, 



B < | lamelliform lateral and nearly obso- 



with teeth _ ot [ lete cardinal teeth Unio fragilis, Sw, 



winded ^ lamel l'f° nn lateral & short cardinal teeth Unio. 



° I lamelliform lateral & long cardinal teeth. Castalia, Lam, 

 (.cardinal teeth only. Alasmodontes. 



Mysca of Turlon is the same as Unio of Authors : his Unio is 

 synonymous with Alasmodon of Say, 



without teeth 



