ANODON purpurascens, 



Furple Anodon, or Horse Mussel. 



Generic Character. — See PI. 96. 



Specific Character. 



A. testa transversim oblongd, crassd, depressd, intus piirpurascetite, 

 lamind cardinali crassd, truncatd, defite lamellari in utrdque valvd 

 supposito; umhonibus retusis. 



Shell transversely oblong, thick, depressed, within purple; hinge 

 plate thick, truncate, with an obsolete lamellar tooth in each 

 valve ; umbones retuse. 



T HIS is an entirely new and very rare shell, remarkable for 

 its shape and internal colour; it is also highly interesting, 

 as exhibiting the generic characters of Aiiodon, blended (in 

 some degree) with those of Unio : according to the principles 

 of Lamarck, it might therefore be made into a genus ; but 

 I feel convinced too much importance has already been 

 attached by that naturalist and his followers to the hinge of 

 bivalve shells ; and that the nomenclature of the science is 

 burthened with genera, trivial in themselves, bewildering to 

 the scientific, and unintelligible to the student. 



From having paid some attention to the Fluviatile Bivalves, 

 and possessing a most extensive collection of specimens, I 

 am clearly of opinion that no permanent characters will be 

 found sufficient to retain either the genera Dipsas (Leach), 

 Hyriu (Lamarck), or Alasmodonta of Say, much less that of 

 Damaris (Leach), and another, whose name I forget, made 

 by Dr. Turton from the same shell as Leach's Damaris, viz. 

 Mya Margaritifera of Linnaeus. In fact, the line of demarca- 

 tion between Unio and Anodon appears to rest on the first 

 possessing cardinal teeth, and the latter having none. 



I have several valves (in different stages of growth), and 

 one perfect specimen of this shell; they were sent to me 

 from the back settlements of North America. 



PI. 160. 



