Coll — The Unionidce of Arkansas. -^5 



beaks, large, often pit-like, in old shells exhibiting two or 

 three large scars, circular in outline, and as deep as the pro- 

 tractor pedis impression, though the posterior one is commonly 

 oval ; plate connecting the cardinal and lateral teeth not well 

 developed ; nacre usually dark purple, often pink, white, or 

 salmon; frequently the coloration is confined to the region of 

 the cardinal and lateral teeth, the remainder of the interior 

 being pure white. 



Length, 171 mm. ; breadth, 60 mm. ; height, 70 mm. 



These are the dimensions of very large shells collected in 

 the Cedar river, Iowa. 



This species ranges from New York to Minnesota, Nebraska, 

 Kansas, Indian Territory and Texas, to Georgia, and is com- 

 mon throughout all that vast area. 



Unio retusus Lamarck. 



Plate VIII. 



Historic Naturelle des Animaux sans Vertebres, 1819, 



Vol. VI, p. 72 ; also, 2d edition, 1838, Vol. VI, p. 534. 



Described as from Nova Scotia. Reeve, in Conchologia 



Iconica, Vol. XVI, Unio Plate LXXI, Figs. 363a, 363b, 



1868. 



Unio torsa Rafinesque. Annales Generales des Sciences 

 Physiques, Bruxelles, 1820, Vol. V, p. 311, Plate 

 LXXXII, Figs. 1, 2 et 3. Described from the Ohio. 

 See also Conrad, in Monograph of Unio, Plate VIII, 1836, 



p. 19. 



Unio obtusa Say. So Deshayes, in Cuvier's Regne 

 Animal, teste Lea. I have been able to find no work in 

 which Say uses this name for any Unio. 

 Lamarck described this shell in the following terms: — 

 " U. testa roiundata, tumida, intus violacea; natihus 

 retusis, erosis; deiite later ali breviusculo. * * * 



Habite les rivieres de la Nouvelle-Ecosse. A. Micliaud. 

 Test epais; epiderme d' un vert jaunatre; dent cardinale 

 grossiere, sillonnee, divisee en deux. Longueur apparente, 

 47 millimetres.'' 



The range of this species is rather more restricted than is 



