LAND AND FRESH-WATER SHELLS. 177 
Specimens, is a method which to my mind is not sufficiently taken 
advantage of by conchologists. The vast number of small shells 
collected and deposited in certain places even by a little stream 
is surprising, but it is considerably less so when we consider what 
a large area its waters cover when in a flooded state, and that all 
small shells float when empty. The principal sorts so to be 
obtained are the Zonites, the smaller Helices and Clausilie, but 
particularly the Pupe and Vertigoes. As my drift for examination 
has been entirely obtained near the city, it cannot well be urged 
that the shells in it have travelled from beyond our boundaries. 
I am far from believing that the list is a complete one, though 
the eighty-nine species, or thereabouts, mentioned make a very 
fair total. I shall always be pleased to hear of any additions. 
I. AQUATIC MOLLUSCA. 
BIVALVES (CONCHIFERA). 
Order LAMELLIBRANCHIATA. 
Fam. SPH#ERIIDE. 
Spherium corneum.— Fine and abundant throughout the 
district generally. The finest specimens I have got near York are 
from Foss Islands (H.) Pale grey variety at Askham Bog (H.) 
Var. flavescens.—Not uncommon. Good at Hobmoor and 
Askham Bog. “Very abundant this year in the lower part of | 
the Foss” (H.) 
Var. nucleus and var. pisidioides.—I have taken both these near 
the city, but cannot name the exact locality. 
Spherium rivicola.—Abundant and fine in the River Foss at 
Blue Bridge (H.) Rare in the Ouse. 
Spherium ovale.—Mr. Hey writes :—“ Abundant and very fine 
in the Foss, burrowing to a depth of several inches in the mud. 
I first found it near Blue Bridge in the summer of 1874; but it 
was nearly killed by a severe frost when the water was let off in 
January, 1880, so that in June following I was not able to find 
any specimens.” 
Spherium lacustre-—A comparative rarity throughout the 
whole York district. I have occasionally obtained it at Hobmoor, 
Askham Bog, Stockton-on-the-Forest, and in the Foss. Common 
in ponds at Rawcliffe, and also in several ponds near Clifton, in 
which it positively teems at times, but at others is scarce (H.) 
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