THE NAUTILUS. 



VOL. XVII. SEPTEMBER, 19O3. No. 5. 



THE SPECIFIC VALUE OF TJNIO DECLIVIS, SAY. 



BY L. S. FKIERSON. 



The synonymy of JJnio tetrctlasnnis Say, given by R. E. Call in 

 the Transactions St. Louis Academy of Sciences, vol. vii, 1895, 

 page 52, has been very generally followed ; wholly by some, and 

 partially by others. Mr. Call says : " It preserves its specific 

 character so generally that it is a matter of great surprise that so 

 many synonyms should fall under it. The study of the figures, 

 descriptions and localities above indicated will furnish convincing 

 evidence of identity. Of the total number [of synonyms] listed 

 seven came from Louisiana and contiguous territory; of these seven, 

 five are from the same state (Louisiana] and of those five two are 

 from the same bayou." I have faithfully studied the descriptions, 

 etc., above indicated, together with the shells themselves in their 

 native habitat, Louisiana, with the result that I find U. dedii'is 

 Say, to be readily recognizable as a perfectly distinct species from 

 the balance of this group, with U. geoinetricus Lea, as a synonym 

 (according to Dr. Lea himself). Unio declivis is, moreover, very 

 rare as compared with the rest of the group, and generally misunder- 

 stood. In order that students may recognize the shell it is figured 

 herewith, and the following specific differences noted: 



First. It never attains the extreme size of U. tetrulasmus as 

 shown by the following measurements, based on adult specimens of 

 each : 



