4 Trans. Acad. Sci. of St. Louis. 



Unio siibovatus Lea was based on the male of Say's Unio 

 ovatus. 



This list, illustrating what appears to have been the misin- 

 terpretation of sexual differences, might be extended indefi- 

 nitely ; when extended to its limits the student of the 

 Vnionida; will be astonished at the results which he will reach. 



Aside from personal collections, made in the intervals of 

 field work in geology, and which were made in the St. Francis, 

 Ouachita and Saline rivers, help has been derived from speci- 

 mens collected by Professor R. T. Hill, in the Ouachita, by 

 Mr. L. S. Griswold, in the Ouachita well up toward its 

 source, and by Mr. F. A. Sampson, in the White river and in 

 other portions of northern Arkansas. Dr. John C. Branner, 

 State Geologist, has furnished an occasional specimen. Other 

 shells have been sent, for identification, from the Little Red 

 river. It is a matter of regret that more full and exhaustive 

 collections could not be made preliminary to a final paper; it 

 would better represent the wealth of the State in this group 

 of natural objects. It will be noticed that three streams and 

 as many localities furnish the major portion of the species here 

 listed. Reasoning from this fact it is fair to assume that very 

 many forms yet remain to be added to the list on complete 

 examination of the State. 



REGISTER OF SPECIES. 



Unio aberti Conrad. 



Proc. Phila. Acad. Nat. Sci., p. 10,(1850); Jour. 

 Phihi. Acad. Nat. Sci., 2d series, Vol. II, Plate XXVI, 

 Fig. 1, (1851). 



(Jnio kimarckianus Lea. Trans. Am. Philos. Soc, 2d 

 series. Vol. 10, PI. 17, Fig. 20, (1852). 



Ujiio 2Jopenoi CiiW. Bulk Washburn Coll. Lab'}' of Nat. 

 Hist., No. II, pp. 48-49, PI. II, (1885). 

 This form was described by Lea from the Caddo river, under 

 the name of Unio lamarcManiis, the specimens of which were 

 submitted to him by Dr. Byrd Powell. Additional examples 

 were submitted by Dr. Hale who collected them in the Ouachita 

 river, near the Hot Springs. The specimen figured by Doctor 



