BIVALVES. 
41 
but easily known by the plate-like projection on 
each valve near the nmbones. 
It occurs in several localities in England and 
in South Wales ; the only Irish locality recorded 
is Finnoe, co. Tipperary. It occurs in the 
newer Tertiaries. 
Pisidium NiTiDUM — (the Shining Pisidium) 
(PI. IV., fig. 22).—Shell suborbicular, very 
shining, finely and regularly striated, with a few 
separate and deeper grooves around the obtuse 
and subcentral nmbones. Length one-twelfth of 
an inch, width one-fifth less. The most obvious 
distinctive characters are its rounded outline, 
glossy and iridescent appearance, the strong 
concentric grooves on the umbonal region, which 
are more readily seen in young shells, and 
the funnel-shaped siphon with its plaited outer 
margin. 
It is somewhat generally distributed in lakes, 
ponds, and pools. Mr. J. Thompson found it 
abundantly in a cold turfy deposit conveyed by 
a mountain stream to a pond near Belfast, and 
on Utricularia vulgaris, growing in stagnant 
pools. These places are of a very different 
nature, the pond at the former being supplied 
with clear spring water, and at an elevation of 
600 feet above the sea; the latter but a few 
feet above it, and supplied only with rain¬ 
water. 
