r 
462 Messrs. TI’. and A. Scott on some 
The antennules are sparingly setiferous, and the long some- 
what slender filament springs from the end of the fourth joint 
(fig. 11). The antenne are slender, and the first and second 
joints are each provided with one seta, while the last bears a 
few sete at the apex (fig. 12). The mouth-organs are some- 
what similar to those of Jdya furcata, but the posterior foot- 
jaws have the terminal claws void of supplementary sete 
(fig. 18). The swimming-feet are also somewhat similar to 
those of Idya furcata, but the second joint of the outer branches 
of the first pair is about twice the length of the first joint, 
and the spine which springs from the outer distal angle of the 
first joint is comparatively slender (fig. 14). The fifth pair 
are also more elongate than those of /dya furcata, being fully 
four times longer than broad (fig. 17). 
Habitat. ast Loch Tarbert, Loch Fyne. Several speci- 
mens of this species were taken with the dredge in 5 to 6 
fathoms water in February 1886, but have not been previously 
recorded. 
Remarks. Idya longicornis is easily recognized, not only 
by its larger size, but also and especially by the length and 
structure of the antennules. ‘lhe proportional lengths of the 
joints of the outer branches of the first pair of swimming-feet 
and the elongate fifth pair also serve to distinguish this from 
any other British form of Jdya. Though this ldya is the 
largest form of the genus with which we are familiar, the 
armature of the first pair of swimming-feet is not so powerful 
as that of the first pair in Jdya furcata, a much smaller 
species. We are not altogether unfamiliar with the lability 
of Juya furcata to variation, and also with the observations 
of several eminent naturalists on this liability to variation in 
Idya furcata; but we have seen no explanation that could 
account for the great differences between Jdya furcata and 
the species we have now described on the principal of local 
variation, for both forms were taken together by the dredge 
on the same ground and at the same time. Had the two 
forms been taken in different localities hundreds of miles 
apart, there might have been some reasonableness in con- 
sidering them merely as varieties of the one species; but, 
taken as they were, under similar conditions of time and 
place, we can only judge of the differences between them as 
we judge of the differences between forms belonging to other 
genera. 
ADDITIONAL NOTES. 
An interesting addition to the freshwater Crustacea of 
Scotland has only lately been obtained, viz. Ophiocamptus 
o «4 es cee 
