LAND AND FRESH-WATER SHELLS. 181 
most of the thick incrustation on their shells. Meat was their 
principal food, and if in a high state of putridity it mattered 
nothing. Young specimens seemed to be far more lively than 
older ones. On one occasion one of my largest specimens under- 
‘went the misfortune of being ejected, and for more than three 
weeks lay on the ground in a field, but upon being restored to its 
fellows seemed to have taken no harm. On May 11th, 1877, 
a young one was born and others followed until the 18th. At 
first each seemed to be enclosed within a ball of slime, but after 
getting free of this was very active. A few years ago the 
number in the River Foss was very limited, but Mr. Hey writes 
that, “Though it continues to abound in the Ouse, by far the 
finest specimens now come out of the Foss, where it has grown 
equally common.” 
Var. albida.—I admit this only with great doubt, there being 
no recorded variety of this name, nor have I ever heard of speci- 
mens, except two in the collection in York Museum. They are 
pure white, rather small, and have “var.” written on their label. 
The late curator, Mr. Wakefield, says they are genuine, and were 
left by Prof. Phillips, but their locality is quite unknown. 
Bythinia tentaculata.—Very common. Foss, Askham Bog, 
Hobmoor, &c. A variety with a single white band occurs at 
Askham Bog (H.) 
Bythinia Leachii.—Common, but not generally of large size, 
in the River Foss. Mr. Hey says only as far up as Huntington. 
Also in a small streain joining the Foss near the third lock. It 
has the power, like most other operculated water-shells, of 
remaining out of water a considerable time, even weeks. 
Fam. VALVATID®. 
Valvata piscinalis.—Abundant in the Foss, from which I have 
a specimen with the whorls much distorted. Ouse at Naburn. 
Also occurs, but rarely, in Askham Bog (H.) 
Var. depressa.— Specimens from York are in the British 
Museum. 
Var. acuminata.—Few in the Foss (R.) 
Valvata cristata.— Pretty numerous in the Foss and its 
small tributary, a few in the Ouse, and very abundant in certain 
ponds at Askham Bog, where Mr. Hey says it is greatly on the 
increase. 
