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. 
This 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 gracilis 
Barnes, and a still more striking likeness to an ‘‘ alasmidonta’’ 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 circumstanee 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 
