+ 
348 On Pisidium supinum and P. parvulum. 
P. supinum in my collection have these teeth quite as much 
separated from the shell-margin as shown in Mr. Phillips’s © 
figure, and instanced by him as characteristic of P. parvulum. 
It is all a matter of sufficient material on which to base 
conclusions, and that at present Mr. Phillips and Mr. Stelfox 
do not seem to possess, and its lack cannot be compensated 
for by zeal even as great as theirs. 
A feature that is of real importance is the character of the 
cardinal teeth in the left valve. In P. supinum the apex of 
c¢ 2 is directed towards the umbo, so that its posterior margin 
seems to directly traverse the hinge-plate, and, ¢4 being 
parallel to it, the effect is given of both teeth lying trans- 
versely to the hinge-line. In P. parvulum, on the other 
hand, these two teeth appear as approximately parallel with 
the shell-margin. 
With respect to P. swpinum, there is no question as to its 
occurrence in the sands named, but there is just a doubt as to 
how it got there. The deposit in which this species was 
first found in Ireland—namely, at Waterford Bridge, by 
Mr. Phillips—contained a specimen of Vivipara, which genus 
has so far not yet been established as Irish, pieces of flint, 
which is not a product of southern Ireland, and the apical 
portion of a Tara inquinata, the well-known fossil charac- 
terizing the Woolwich beds, which certainly are altogether 
unknown in Ireland. Moreover, since the mineralization of 
the specimens of P. supinum and some other shells in the 
deposit differed from that of the rest and agreed exactly 
with the state of preservation of the shells in the Thames 
Holocene sands, the inference was irresistible that they had 
been introduced in ballast. 
Mr. Phillips pleads in correspondence that the Fiddown 
deposits, being 15 miles higher up the river, where no boats 
with ballast go, this possibility of introduction is precluded. 
In view of the facts above recited, however, and remembering 
that trade with Ireland has been going on for many centuries, 
during the greater part of which time small sailing vessels 
would be employed that could proceed higher up stream, the 
possibility of importation is not lightly to be ignored. 
Moreover, in the days before half-hundredweights or bars of 
iron were available with which to trim the boat, and in the 
absence of rocks from the Thames foreshores, what more 
likely than that bags filled with river-sand should be employed. 
In short, stronger proof than is at present adduced should be 
offered ere the claim that P. suptnum is indigenous in Ireland 
can be established. 
