THE NAUTILUS. 135 
bridge at that point. Here, and for a distance of two and a half miles 
above it, the small stream, to which the ‘‘back river ’’ dwindles at ex- 
treme low water on the south side of Neville Island below the wing 
dam, is more or less thickly populated with living uniones. This stream 
is supplied almost wholly by fresh water springs rising along its 
bottom. From the absence of live mollusks in any part of the main 
river and other parts of the “back river” where these fresh springs 
exert no influence, it is just to conclude that to these alone is due the 
existence of the only living uniones which I was able to locate in 
Allegheny county. A special collecting trip for mussels was taken 
to Beaver, Beaver county, search being made in the Ohio river at the 
junction of Beaver river, and at several points below Beaver to the 
mouth of Raccoon creek and up that creek two miles. Living shells 
were very scarce anywhere along this route, most of them being taken 
where the less polluted waters of the Beaver joined those of the Ohio. 
Below this, along the bed of the Ohio, nearly all the uniones found were 
dead or dying, a condition of affairs which the ferryman at Vanport told 
me had come to pass largely in the last two years. The subjoined list will 
also contain an enumeration of the species found during a day’s hunt 
in the Beaver river below Wampum, in the southern border of Law- 
rence county, about fifteeen miles north of Beaver. The conditions 
obtaining among the water mollusca in that locality are probably 
normal. 
Mr. Clapp has kindly consented to read the manuscript of this paper 
and make such annotations as may be Sf special interest. To such 
notes his initials areappended. In the Mentification of this collection 
the author was accorded every facility afforded by the collection of 
uniones in the Carnegie Museum, identified by Mr. Simpson and by 
the historic collections of the Academy of Natural Sciences, where the 
final determinations were made. To Dr. W. J. Holland, of the 
former, and Prof. Henry A. Pilsbry, of the latter, [ am especially in- 
debted for services rendered in this connection. For sake of conven- 
ience in reference the nomenclature of Lea’s Synopsis (1870) is 
adopted for the Uniones; and the sequence of the genera and species 
of Unionide is alphabetic. 
Annotated List of Species. 
Family Unronrpar. 
Anodonta edentula Say. Ohio R., Coraopolis, 16; Beaver, 1 : 
Beaver R., 14. 
