COMMUNICATIONS 
TO THE 
MONTHLY MEETINGS 
OF THE 
YOEKSHIEE PHILOSOPHICAL SOCIETY, 
1882. 
March 7th, 1882.—The Eev. W. 0. Hey, AI.A., read the 
following paper on “Fresh-water Mussels in the York Eivers.” 
The Ouse and the Foss, which unite just below York at the 
spot known as the Blue Bridge, are rivers of very different 
character, much more so than the superficial observer would 
suppose. The Ouse is a wide, deep, and generally rather a rapid 
river, sometimes, in floods, almost a torrent. The Foss is a 
narrow river, natinally shallow, though in parts deepened artifi¬ 
cially, and the current flows so gently that often the water is 
practically stagnant. Again, the Ouse has a very hare channel 
somewhat hard and stony in places, and even where the bottom 
is soft and sandy there is no vegetable growth. But the Foss has 
a bottom of rich soft mud, where the flags and the water-lilies 
root themselves and flourish luxuriantly. In places the river is 
quite overgrown with tall rushes in summer time. Again, the 
Ouse receives a good deal of drainage, the Foss not much, except 
one very poisonous kind, viz., that which escapes the Gras Works. 
Once more, near York the Ouse has no locks. This is a very 
important point to notice in regard to the distribution of species. 
But the Foss has three locks within the space of as many miles 
viz., Castle Mills Lock, Yearsley Lock, and Huntington Lock. 
Asking you to bear in mind these points of contrast between the 
Ouse and the Foss, I go on to make a few remarks on the genera 
and species of mussels found in these rivers. The family of 
TJnionidce or freshwater mussels is represented in England by two 
