THE FAMILY NAIADES. 



135 



TRIANGULAR. 



*carnelus. Lea. 



*ovatus. Say. Lam. Bar. Valen. 

 Eat. Hild. Con. 

 Unio ventricosus. Desh. 

 Unio subovatus, Desh. 

 Unio occidens. Desh. 



*subovatus.f Lea. 



*crassidens4 Lam. 



Uaio cuneatus. Bar. Eat. Hild. 

 Unio nigerl Raf. 

 Unio niger. Con. 



*carbonarius. Lea. 



*gibber. Lea. 



*pumilis. Lea. 



*rubigino3us. Lea. 

 *Barnesianu3. Lea. 



a 

 2 < 



TRIANGULAR. 



*pileus. Lea. 

 *Sowerbianus. Lea. 

 *trigonus. Lea. 

 *solidus. Lea. 



*obliquus. Lam. 





Unio imdatus. 



Bar. 



Unio trigonus.§ 



Say and Con. ; net 



of Lea. 





Unio mytiloides. 



Eat. 



Unio undulatus. 



Desh. 



Unio cordatusl 



Raf. 



Unio cordatus. 



Con. 



*pyramidatus. Lea. 

 Unio rubra 1 Raf. 

 Unio mytiloides. Con. 



*mytiloides.|| Raf. 



Mya obliqua. Wood. 



Raf. Mr Say does the same, with the exception of ellipsaria, which he considers distinct ; while Mr Rafinesque 

 himself places lineolata and ellipsaria in different subgenera ! ! 



t Mr Say makes " ventricosus, Bar., occidens (nobis), subovatus {x\6b\s), (var.), and capax. Green, (var.)," 

 synonymous with cardium, Raf. In my opinion they form at least three, perhaps four distinct species. 



J Crassidens, Var. a, Lam., is trapezoides (nobis). 



§ Say and Conrad both give trigonus (nobis) as a synonym to undatus, Barnes. It is difficult for me to 

 understand why they should not at once on comparison be recognised as different species. The trigonus is 

 always more angular on the umbonial slope, and the undulations at the tips of the beaks differ. This may be 

 observed particularly in the young and perfect specimens. If a doubt could be admitted as to the difference of 

 the form of the shell, the colour of the animal in trigonus would at once settle the question. It is peculiar, and 

 differs from all the species I know in being of so deep a colour as to be almost red. 



Some years since, when I described this species, I deposited a specimen in the Academy of Natural Sciences 

 of this city, with its proper name appended. Subsequently, I found the Academy had prefixed the name of 

 undatus, Barnes, to the label, and I presume this error is still continued there. 



II It is a matter of great doubt if this name ought to be admitted at all in this table. It was applied many 

 years since, by the naturalists of this city, without reference to any particular specimen, but, as it now appears 

 nearly certain, incorrectly. Dr Ward says the description and outline would " equally well apply to six or 

 eight different species." The difficulty of recognising Mr Rafinesque's species is well illustrated in this one. 

 Mr Conrad considers triangularis, Raf., as the type, and gives the following names of the same author as sy- 

 nonyms, viz. lateralis, sintoxia, pachostea, mytiloides, and rubra', thus charging him with making six species 

 of one. But what is still more extraordinary, this single species, (agreeably to Mr Conrad's synonyms) is not 

 only divided by Mr R. into different subgenera, but into different genera, and even into two different sub- 

 VI. 2 G 



