12 Trans. Acad. Sci. of St. Louis. 



streams of north-central Alabama, notably in the Coosa, 

 Alabama, and Cahaba rivers. 



A good illustration of this form may be found in Conrad's 

 Monograph, PL III, fig. 1. Also in Tenney's Zoology, 

 Manual, edition of 1872, p. 492, Fig. 460. Reeve, Concholo- 

 gia Iconica, Plate LXIX, Fig. 354, also well exhibits its chief 

 features, but the beaks are represented to be more decurved 

 than in any specimen we have ever seen. 



Unio cornutus Barnes. 



Am. Jour, of Sci. and Arts, 1st series, Vol. VI, p. 122, 

 Fig. 5a, 56, 1823; 



Unio refiexus Rafinesque, in Conrad's Monograph, PL 

 IV, Fig. 1, 1838. 

 This species has been seen by us from only one Arkansas 

 locality. That one was the St. Francis river, at Wittsburg, 

 in Cross count3^ It has a wide range in its geographical dis- 

 tribution since it occurs from western New York to Kansas 

 and south to Alabama and Texas. 



Unio crassidens Lamarck. 



Plate II. 



Unio m^er Rafinesque, in Conrad's Monograph of Unio, 

 PL XXVI, 1836. 



Unio incrassatus Lea. Trans. Am. Philos. Soc, 2d 

 series. Vol. VIII, PL XVI, Fig. 34, p. 217, 1840. 



Unio Guneatus Barnes, Am. Jour, of Sci. and Arts, 1st 

 series. Vol. VI, p. 263, 1823. 

 Lamarck's description included several varieties, some of 

 which were improperly included in the species as limited. 

 Such, for instance, is his variety a which is said by Dr. Lea, 

 who saw the type in Paris, to be his Unio irapezoides and 

 which is entirely distinct from crassidens. The original 

 description here follows from the Ani7naux sans Vertebres, 

 2d Edition, Vol. VI, p. 532, 1838. 



'< U testa ovali, tuinida, crassa, postice rotundata, antice^ 

 angidis binis iernisve subsinuosa, dente cardinali crassissimo 

 lobato, angidato, striato. 



