THE NAUTILUS. 129 



Finally, we observe that Rafinesque in his description of a 

 variety of " alasmidonta " wrote that the latter is so much like 

 Unio viridis, as to be easily mistaken for it for which cause he 

 named the shell Alasmidonta viridis. 



Ihis statement may be compared with an observation made by Mr. 

 C. T. Simpson, who wrote that the ' ' Unio pressus Lea, and the 

 Margaritana rugosa Barnes sometimes resemble each other so much 

 that one is labeled with the name of the other by competent students. ' ' 



An Ohio shell, of subsolid texture, elliptical in shape, with 

 an oblique posterior truncature; green, sometimes brownish, 

 sometimes rayed with yellow; having its beaks crowned with 

 flexuous wrinkles; a cardinal tooth thin, compressed and decur- 

 rent, bearing an outward similitude to the old Unio gracilu 

 Barnes, and a still more striking likeness to an " alasmidonia " can 

 but be, the writer thinks, the Symphynota compressa Lea. 



The main objections offered by Mr. Walker for his "inter- 

 ference" arose from the failure of his records to show that the 

 compressa Lea ever occurs in the Ohio River the shell, Mr. 

 Walker informs us, being "most emphatically a creek or small 

 river species. ' ' 



Mr. Walker's records however might be profitably amended by the 

 inclusion of the interesting circumstance that the type locality of Lea's 

 Symphynota compressa 'is the Ohio River at Cincinnati (Index 

 Obs. Genus Unio). 



Mr. Walker's "reason No. 4' is a slight variant of a state- 

 ment made by Dr. Lea (Rectification, P. 35). 



If Conrad and Say radically differed as to what an identical 

 valve was (which it is said was seen by both) the writer fails to 

 see how their disagreement should be chargeable to Rafinesque' s 

 diagnosis of the Unio viridis. 



Walker's "reason No. 5" need be discussed no longer, as it 

 was categorically rejected by Dr. Lea long ago (Rectification, 

 P. 34) with whom the writer is heartily in accord. 



The writer has seen it stated that the ratio which the altitude 

 bears to the length, given by Rafinesque for viridis (5 to 9) 

 does not agree with specimens of Symphynota compressa. 



Mr. C. T. Simpson (Catalogue, 1914} gives dimensions of 

 three examples of the compressa. The writer takes it, that the 



