I02 
Tlie Irish Naturalist. 
PisiDiUM supiNUM A. Schmidt 
(Plate II., figs. I to 6.) 
Numerous examples of this species were found in the 
Suir deposit. The shell is triangular in outline, though 
somewhat more rounded than specimens I have seen from 
the Thames, with very strong hinge and prominent umbones 
which are capped by appendiculae. In proportion to its 
size it is one of the heaviest and most solid of our freshwater 
bivalves. It is described in detail with copious illustrations 
by Mr. B. B. Woodward in his Catalogue.^ 
In the Suir sands it is accompanied by a thickened 
triangular form of P. casertaniim w^hich superficially 
resembles it closely, and by a similar heavy triangular form 
of P. amnicum. The presence of these peculiar forms in 
the Suir is remarkable, as the occurrence of a corresponding 
group in the Pleistocene deposits of the Thames Valley 
has been recorded by Mr. Woodward, and recently Mr. J. 
E. Cooper has sent me living examples of the three taken 
together in the Thames at Hampton Wick, Middlesex. 
It is not always easy to separate these triangular specimens 
of P. casertanum from P. supinum, especially if, as it is 
stated sometimes happens, though I have not seen it, the 
appendiculae are absent from the latter, but a good test, 
pointed out by Mr. Stelfox, is the ligament pit which in 
P. casertanum is broad and curved, in P. supinum narrow 
and straight and possesses a strongly-marked ridge running 
along its ventral edge. 
So far, P. supinum has been found only in the Suir 
deposit, all the specimens being separate valves. The 
state of preservation of some of these valves looks as if 
they were not long dead, so it is quite probable that the 
species will be found living in some part of the river when 
looked for. These Irish specimens are undoubtedly native. 
P. supinum was first noticed in the British Islands in 1901 
when dead shells were found on the foreshore of the Thames 
near Kew Gardens, later it was recognized as a fossil in 
many Pleistocene and Holocene deposits in England, and 
1 B. B. Woodward, F.L.S., Sec, " Catalogue of the British species of 
Pisidium (Recent and Fossil) in the British Museum (Natural History) 
with notes on those of Western Europe." London, 1913. • 
