PEISODOX 



27 



II. SUBGENUS PRISODOX. 1 



C TRIANGULAR. 



*truncatus. Schum. 



Cast, ambigxuj,. Lam. D'Orb. Cuv. 



Sow. Guerin. Pot. Schum. 



Sicain. Chenu. 

 Cast, quadrilatera. D'Orb. 1 

 Cast, inflata. D'Orb. 

 Cast, twrgida? Hupe. 

 Cast, retusa. Hupe. 

 Cast, acuticosta. Hupe. 

 Cast, multi sulcata. Hupe. 

 Cast. Castelnauii. H>/j" : . 

 Cast. Crossiana. Hidalgo.* 

 Cast, cordata. Hump. H. & A. 



Adams. 



f TRIANGULAR. 



Unio ambigua. Slain. Desk. Sow. 

 Mya ambigua. Wood. 

 Tetraplodon pectinatum. Spix. 



I 



nodulosus. 5 Wood. 



Mya nodulosa. Wood. Dill. 

 Chama plumbea. Muhlf. 

 Unio plumbeus. (Imp. Cab. iu Vien- 

 na.) 



Duprei. Recluz? Chenu. 



1 Schumacher, in his Nouceau Systeme, 1817, p. 138, formed the genus Prisodon, in which he included 

 the two now well known shells Hyria syrmatophorus and Castalia ambigua. His name for the first can- 

 not be applied, as Klein, in 1753, preoccupied this genus by naming it Triquetra. Therefore it must be 

 applied to Castalia, which name was given to the same shell by Lamarck in 1819. Mr. Gray, in his 

 ^'Genera," gives Schumacher priority in the name of Prisodon, in which he is perfectly correct. 



2 I owe to the kindness of M. D'Orbigny specimens of this and inflata. I regret, however, that I 

 am compelled to differ in opinion with this distinguished naturalist, believing, as I do, that there have 

 been as yet observed but three species of Prisodon (Lamarck's Castalia). 



3 1 have all these five forms of M. Hupe's in my collection, and have always esteemed them the 

 truncatus Schum. 



4 1 have seen no specimen, nor has M. Hidalgo given a figure; but I suspect that Crossiana is a more 

 perfect specimen of ambigua than usual. I may, however, be entirely mistaken in this oinnion. 



5 In my second edition, p. 22, this shell was placed among the Uniones, with a note as to its analogues 

 and its habitat. On my visit to Yieuna in 1853, I found, in the Imperial cabinet, the right and left valves 

 of two individuals under the name of Chama plumbea Miihlfeld, but then labelled Cnio plumbeus. Having 

 serrated teeth, it properly belongs here. See Proc. Acad. Nat. Sci., vol. 6, p. 368. 



6 A tine specimen is in the museum of the Academy of Natural Sciences of Philadelphia. 



