UNIO. 



25 



TRIANGULAR. 



*Sovrerbianus. Lea. Con. Kiist. 

 *trigonus. Lea. Chenu. 

 *Rajahensis. Lea. Chenu. 

 cyrenoides. Phili. 

 *Holstonensis. Lea. Chenu. 



- 



*tumescens. Lea. 



o - 

 o 



*fulgidus. Lea. 





*solidus. Lea. Chenu. 





*obliquus. Lam. MenJce. 





Unio undatus. Bar. Hild. Kiist. 





Unio trie/onus. 1 Say. Con.; not of 





Lea. 





Unio mytiloides. Eat. 





Unio undulatus. Lesh. 





Unio cordatusf Raf. 





Unio cordatus. Con. Kiist. 



- 



Unio caridiacea. Guerin., 



TRIANGULAR. 



*plenus. Lea. 



*pyramidatus. Lea. Kiist. Chenu. 

 Unio rubra? Raf. 

 Unio mytiloides. Con. 

 Unio cardiacea. Lesh. 



*Bournianus. Lea. Chenu. 



*Edgarianus. Lea. Chenu. 



*mytiloides. 2 Raf. Swain; not of 

 Lesh. 

 Mya obliqua. Wood. 

 Uniopsis mytiloides. Swain. 



OBLIQUE. 



*Troostensis. Lea. 

 Unio trabalis. Con. 



*trossulus. Lea. 



* Tigris. Fer. 



*Taitianus. Lea. 



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

 understand why they should not at once, on comparison, be recognized 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 color 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 color 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. 



a 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 recognizing Mr. Rafinesque's species is well illustrated in this one. Mr. Con- 

 rad considers triangularis, Raf., as the type, and gives the following names of the same author as synonymes, 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 synonymes) is not only divided by 

 Mr. R. into different subgenera, but into different genera, and even into TWO different sub-families ! ! See 

 New Fresh Water Shells of the United States, p. 72, and Mr. Rafinesque's Monographie. In Mr. Say's Synonymy, 

 triangularis, Raf., is considered to be the same as ellipsis (nobis) ! Deshayes described a different shell under the 

 name of mytiloides. {Ency. Meth. p. 249, Fig. 4.) I doubt from this figure if it be not a complanatus. We cer- 

 tainly have in our rivers, occasionally, specimens of this protean species very closely resembling this figure. It 

 also has some resemblance to an imperfect Batavus. The habitat is not known. 



7 



