THE NAUTILUS. 



121 



Strophitiis edentulus (Say). Ouachita River and Old River. 

 In the latter locality specimens are quite thick and heavy. 



Anodonta imbecilis Say. Ouachita River, Arkadelphia, Old 

 River, and Deceiper Creek and Gum Springs. Common. 



Anodonta suborbicidata Say. From Old River only. The 

 young are perfect and most beautifully rayed. In the lower 

 channel of the "river" they attain an unusual size. 



Anodonta grandis leonensis (Lea). Ouachita River, Arkadel- 

 phia, and Old River. One must go deep in the mud for these 

 fine shells but they are fairly common. 



Anodonta virens Lea, var. Ouachita River and Old River, 

 Arkadelphia. Distinguished from leonensis by having much 

 higher and more prominent beaks, and by being less elongated. 



Arkansia ivheeleri, Walker and Ortmann. Old River and 

 (rarely) Ouachita River below Arkadelphia. This is likely to 

 remain one of the rarest of Unios. The nacre of this species is 

 one of its most attractive characteristics. In young shells the 

 entire margin is widely bordered with a rich salmon, in most 

 adults it is a warm cream color, while in some specimens it is 

 an opalescent blue. In very young specimens the plications are 

 sometimes entirely wanting, but it could not be mistaken, even 

 then, for any other species. Pearlers sometimes open this shell 

 mistaking it for Quadrula pustulosa (Lea). 



Symphynota costata (Raf. ). Ouachita and Old Rivers, but very 

 rare indeed. This species is quite common, however, in the 

 Saline River (at Benton), and it has been a surprise not to find 

 it more abundant in the Ouachita. It is also common in the 

 Caddo far up in Montgomery County. 



Symphynota complanata (Bar.). One specimen only was col- 

 lected in 1913 in the Ouachita River below Arkadelphia. This 

 and Cumberlandia monodonta (Say) remain the rarest of all the 

 Unios in this region. 



Cumberlandia monodonta (Say). Ouachita River above Skil- 

 lern's Shoals, Arkadelphia. This record extends the range of 

 this species much further to the southwest than was to be ex- 

 pected, for heretofore it has not been known west of the Missis- 

 sippi south of Iowa! A full discussion of the distribution will 

 be found in Walker's " Distribution of Margaritana margaritifera 



