THE NAUTILUS. I;;; ( 



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 yery 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 of special interest. To such 

 notes his initials are appended. In the identification of this collection 

 the author was accorded every facility afforded by the collection of 

 uniones in the Carnegie Museum, identified by 31 r. 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, I 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 Unionidse is alphabetic. 



Annotated List of Species. 



Family UNIONIDAE. 



Auffdonta edentula Say. Ohio R., Coraopolis, 16; Beaver, 1 .^ 

 Bearer R., 14. 



