Call — TTie Unionidce of Arkansas. 47 



has several folds or plications, rather thin ; anterior cicatrices 

 distinct, deep and pit-like, not very large, the adductor rough- 

 ened, the protractor pedis striate; posterior cicatrices deeply 

 impressed, large, confluent, that of the retractor pedis at the 

 tip of lamellae of lateral teeth ; dorsal cicatrices numerous, 

 pit-like, often confluent, placed on the plate formed by the 

 base of the cardinal teeth ; pallial cicatrix well impressed 

 throughout, but deepest and most crenulate anteriorly; nacre 

 rich purple, lighter to white on the margins, beyond the 

 pallial line. 



Length of a mature specimen, 70.75 mm.; breadth, 43.50 

 mm. ; height, 74.56 mm. 



The species has not yet been found, to our knowledge, in 

 Arkansas; the conditions which obtain in the bayous along the 

 Mississippi are such, however, that it may reasonably be 

 expected to occur since it is common in the Mississippi river 

 farther to the north. 



Unio rotund ATU8 Lamarck. 



Plate IX. 



Animaux sans Vertebres, in Historie Naturelle, 1819, 

 Vol. VI, p. 75 ; also, same, edition of 1838, Vol. VI, p. 

 538. From unknown locality. 



Unio suborbiculatus Lamarck, Historie Naturelle Ani- 

 maux sans Vertebres, Vol. VI, p. 81 ; also 2d edition, 

 1838, Vol. VI, p. 546. From locality unknown. 



Unio glehulus Say. Transylvania Journal of Medicine, 

 Vol. IV, p. 526, 1831 ; also American Conchology, 1832, 

 Plate 34, female ; Reeve, Conchologia Iconica, Vol. XVI, 

 Unio Plate LXXIV, Fig, 384, young and not char- 

 acteristic female. Described from the Bayou Teche, 

 Louisiana. 



Unio subglobosus Leu. Trans. Am. Philos. Soc, Vol. 

 V, 1837, p. 30, PI. II, Fig. 3; Reeve, Conchologia Iconica, 

 Vol. XVI, Plate Unio LXIV, Fig. 321, 1868. Described 

 from the Bayou Teche, Louisiana. Reeve's figure is that 

 of an old male. 



