122 



THE NAUTILUS. 



in North America", Proc. Mai. Soc, IX, June 1910, pp. 137- 

 139; and in 11 Notes on the Distribution of Margaritana mono- 

 donta (Say)", Nautilus, Vol. XXV, pp. 57, 58. For the 

 generic data consult Ortmann, " Cumberlandia, a New Genus 

 of Naiades", Nautilus, Vol. XXVI, pp. 13, 14, where this 

 species is made the type of the genus. 



Alasmidonta marginata Say. Ouachita River below Arkadel- 

 phia; Skillern's Shoals; Old River. This is also a rare species 

 in this region. 



Unio gibbosus subgibbosus (Lea). Ouachita River, Arkadelphia 

 and Skillern's Shoals; Old River. All specimens collected have 

 given to this variety, though some approach very closely Simp- 

 son's delicatus. 



Uniomerus tetralasmus (Say). In " sloughs" and shallow 

 ponds near Arkadelphia, and in Big Deceiper Creek at Gum 

 Springs. Not found in any of the larger streams. It is common 

 in Malvern Creek, at Malvern, Hot Springs County. 



Pleurobema pyramidata (Lea) . Ouachita River, Arkadelphia, 

 and Skillern's Shoals; Old River. Common, attaining, in quiet 

 waters, a splendid development. 



Pleurobema friersoni (B. H. Wright). Ouachita River, Arka- 

 delphia and Skillern's Shoals; Old River. The nacre of these 

 shells is often a beautiful rose or pink, but more commonly 

 white. They were formerly considered to be ridellii, but it is 

 now agreed to refer them to friersoni, though they are not alto- 

 gether typically that species. See Nautilus, Vol. XXVIII, 

 pp. 30, 31. 



Crenodonta perplicata (Con.). Ouachita River, Arkadelphia 

 and Skillern's Shoals: Old River; Caddo River. In Old River 

 this species attains great size, and there is little erosion on the 

 beaks even in the largest specimens. Dr. Ortmann reports 

 finding an Ouachita female (Old River), collected June 29, 

 1911, with glochidia, a very early date. See Nautilus, Vol. 

 XXVIII, p. 21. 



Crenodonta undulata (Bar.). Terra Noire Creek at Mt. Zion. 



Crenodonta trapezoids (Lea). Ouachita River, Skillern's 

 Shoals and near Arkadelphia; Old River. Common. 



Qaadrula cylindrica (Say). Ouachita River, Skillern's Shoals 



