Call — The Unionidoe of Arkansas, 31 



Unio obliquus Lamarck. 



Plate IV. 



Historie Naturelle des Animaux sans Vertebres, 1818, 

 Vol. VI, p. 72; also same, edition of 1838, Vol. VI, 

 p. 534. 



Unio undatus Barnes, inpartwi. Am. Jour, of Sci. and 

 Arts, 1st series. Vol. VI, 1823, p. 121, Fig. 4. From 

 the Wisconsin and Fox rivers. 



Unio cordatus Rafinesque, so Conrad, in Monograph of 

 Unio, p. 48, PI. XXV, 1836; also Reeve, Unio Plate 

 LXXIII, Fig. 376, 1868. 



Unio obliquus Lamarck, so Conrad Monograph PI. 

 XLin, Fig. 2, 1838. Conrad is in error in making 

 ehenus Lea a synonym of this form. 

 Much confusion exists regarding this species, which is a 

 highly characteristic one. Very much more extensive collect- 

 ing than has hitherto been done by any person or organization 

 throughout the range of the form will be needed to place it 

 properly. Whether Unio pyramidatus Lea and Unio mytil- 

 oides Rafinesque may not also fall under it as synonyms could 

 not now be gainsaid. 



Lamarck's original description was as follows : — 

 " U. testa suhlongitudinali, ovato-rotundata, obliqua, sub 

 epiderme Candida; ligamento subduplici; dentc cardinali 

 crasso, sulcato, bipartito. 



a * * * Habite la riviere de VOldo. A. Michaud. 

 Disiincte de la precedents par sa forme: elle est renjiee vers les 

 crochets, deprimee vers V autre extremife, bisillonnee sur le cote 

 anterieur. Longueur apparente, 61 millimetres,'' 



The following description is based upon specimens taken 

 from the Cumberland river, at Nashville, Tennessee, where 

 the species is very abundant, and attains a very large size : — 

 Shell heavy, sulcate, thick, large, triangularly cordate, 

 wrinkled parallel with the lines of growth, compressed on the 

 posterior umbonal slope, turgid or swollen at the umbones, 

 very solid and thick anteriorly ; epidermis rather thick, 

 striate, especially at the margins, black or reddish corneous, 

 olivaceous in the young, eradiate; lines of growth numerous, 

 well impressed, crowded confusedly ; dorso-posterior maro"in 



