120 



THE NAUTILUS. 



Skillern's Shoals and Old River. This species and Nephronaias 

 ligamentina are the most prolific shells in the river. The epi- 

 dermis of castanea is a most beautiful silken black, sometimes 

 with a deep purple bloom, but young shells are yellowish brown 

 and frequently rayed ! 



Amygdalonaias securis (Lea). Ouachita River below Arka- 

 delphia, Skillern's Shoals, and Old River. This is considered 

 a pearl shell. Very fine specimens are from Old River. 



Amygdalonaias elegans (Lea). Ouachita River below Arka- 

 delphia, Skillern's Shoals, and Old River. Quite common. 



Amygdalonaias donaciformis (Lea). Found only in one bed 

 below Arkadelphia and in the swift current at Skillern's Shoals. 

 Later at Old River. 



Tritogonia tuberculata (Barnes). Ouachita River, Skillern's 

 Shoals and below Arkadelphia; Old River; Terra Noire creek. 

 The river specimens are much inferior in size to those collected 

 in the Tennessee drainage. 



Tritogonia nobilu (Con.). Old River. Rare! Simpson now 

 places this species as given. 



Cyprogenia aberti (Con.). Ouachita River, Skillern's Shoals, 

 and in many beds below Arkadelphia. Specimens are not as 

 large as typical aberti, and may eventually be referred to the 

 variety lamarckiana Lea. 



Cyprogenia aberti lamarckiana (Lea). Ouachita River, Arka- 

 delphia. This was also collected in the Caddo River in Mont- 

 gomery County. 



Obliquaria rejlexa Raf. Ouachita River below Arkadelphia, 

 Skillern's Shoals, Old River. The young are, in these locali- 

 ties, beautifully sculptured. 



Ptychobranchns phaseolus (Hild). Ouachita River, Arkadel- 

 phia, and Skillern's Shoals; Old River. It is fairly common on 

 the rocky shoals, sometimes on the sand bars. There seems to 

 be no dividing line between this species and its variety clinton- 

 ense, Simp. 



Ptychobranchns clintonense Simp. Ouachita River above and 

 below Arkadelphia, but not in Old River. Typical specimens 

 with wavy lines are more common at Skillern's shoals. Dr. 

 Walker is disposed to refer all Ouachita forms to clintonense. 



