Call — The Unionidce of Arkansas. 57 



common Unios in North America. Conrad figures this 

 shell as Unio costatus Rafinesque, on Plate VII of his Mono- 

 graph . 



Unio venustus Lea. 



Trans. Am. Philos. Soc, Vol VI, 1834, p. 4, PI. II, 



Fig. 4 ; Reeve, Conchologia Iconica, Vol. XVI, Unio 



Plate LXIV, Fig. 326. Described from Potosi. Missouri. 

 Unio pleasii Marsh. The Nautilus, Vol. V, No. 1, p. 



2, May, 1891. Described from the Little Red river, 



Van Buren county, Arkansas. 

 Specimens have been seen from the Little Red river — the 

 lot forming the types of Marsh's supposed new form, and from 

 the White river, Carroll county. While the species does pre- 

 sent some features, like those of the young of Unio ligamentinus 

 Lamarck, it is entirely distinct from that shell; the compari- 

 son was not fortunate, for very many characters that are not 

 allied to those of the Lamarckian form are exhibited; among 

 them may be mentioned the capillary character of the rays, 

 their wavy outlines, their crowding, also the character of the 

 teeth, which are unlike those of young ligamentinus, the beaks, 

 which are more elevated ,the emarginate character of the female, 

 which is not like the outline of the female ligamentinus. The 

 shell which most nearly represents this one is Unio spatulatus 

 Lea, but it appears to be distinct from it. Having seen 

 and compared the types of Unio pleasii with the real venustus 

 there is no hesitation in uniting them. 



Unio ventricosus Barnes. 



Am. Jour, of Sci.and Arts, Vol. VI, 1st series, 1823, 

 p. 267, Figs. 14a, 14b, 14c; Reeve, Conchologia Iconica, 

 Vol. XVI, Unio Plate XLIII, Fig. 235 ; American Con- 

 chology, Say, Plate XXXII. Described from the Wis- 

 consin and Mississippi rivers. 



Unio occidens~Lea. Trans. Am. Philos. Soc, Vol. Ill, 

 1829; p. 435, PI. X, Fig. 16. Described from the Ohio 

 river. 



Unio cardium Rafinesque. So Conrad, in Monograph 

 of Unio, 1834, p. 7. 



