Call — The Unionidce of Arkansas. 17 



Unio truncatus Rafinesque, Say in American Conchol- 

 ogy, PI. 67. 

 The only Arkansas locality where this form has been found 

 is the St. Francis river, at Wittsburg. It is there a very 

 common shell, preferring rather muddy bottoms. The illus- 

 tration given by Reeve is a fairly good one, but presents certain 

 artistic effects that are not to be seen in the shell itself. It is 

 a member of a group of which Unio donaciformis Lea may be 

 considered a leading term. 



Unio gibbosus Barnes. 



Am. Jour. Sci. and Arts, 1st series, Vol. VI, PL XI, 

 Fig. 12, 1823. 



Unio arctior Lea. Trans. Am. Philos. Soc, Vol. VI, 

 p. 10, PL IV, Fig. 10, 1834; Conchologia Iconica, Reeve, 

 Unio Plate LXXXV, Fig. 454, 1868. 



Unio dilatatus Rafinesque, so Conrad in Monograph, 

 Plate XXI, 1838. 



Unio stonensis Lea. Trans. Am. Philos. Soc, Vol. 

 VIII, p. 195, PL VIII, Fig. 5, 1840; Conchologia 

 Iconica, Reeve, Unio Plate LXXXV, Fig. 453, 1868. 



Unio gibbosus Barnes, so Reeve in Conchologia Icon- 

 ica, PL LXXIII, Fig. 377. 



The figures of all these forms, as given by Reeve, are poor 

 and do not well represent the shells. U. stonensis Lea is from 

 Stone river, Tennessee, from which original locality the 

 writer has specimens, and these are part of the original lot, 

 identified by Mr. Lea, and still with the name in his handwrit- 

 ing. They formerly belonged to Dr. Troost, of Nashville, 

 and were douated by Dr. J. Berrien Lindsley, into whose 

 hands many of the shells of the Troost collection passed. 

 There is no question that the form from the Ohio, which Mr. 

 Lea called Unio arctior, is a white-nacred variety of gibbosus, 

 a form which is commonly marked by a purple nacre. The 

 white-nacred form, or arctior, is common in the Saline river, 

 at Benton; it is abundant also in the Piney river, Missouri. 

 Typical gibbosus was obtained in the St. Francis, at Witts- 

 burof. 



