Call — The Unionidce of Arkansas. 81 



Unio obliquus Lamarck. 



Plate IV. 



Historic Naturelle des Animaux sans Vertebres, 1818, 

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

 p. 534. 



Unto undatus Barnes, inparlim. Am. Jour, of Sci. and 

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

 the Wisconsin and Fox rivers. 



Unio cordatus Rafinesque, so Conrad, in Monograph of 

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

 LXXIII, Fig. 376, 1868. 



Unio obliqiius Lamarck, so Conrad Monograph PI. 

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

 ebenus 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 U7iio 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 sublongitudinali , ovato-rotundata^ obliqua, sub 

 epiderme Candida; ligamento subduplici; dentc cardinali 

 crassOy sulcato^ bipartite. 



«* * * * Habite la Hviere de V Ohio. A. Michaiid. 

 Distinct e de la precedents par sa forme: elleest renjlee vers les 

 crochets^ deprimee vers V autre extremite^ bisillonnee sur le cote 

 anteHeur. 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 urabonal 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 margin 



