NEBALIA. 
37 
rather long, and furnished at extremity with one long 
slender, and three or four short setae, not plumose. 
Length, three eighths of an inch. 
Montagu describes his species as possessing only three 
pairs of natatorial feet, and in his figure represents them, 
as well as the antennae and caudal appendages, as very 
hairy. 
Leach describes his as having five pairs of natatorial 
feet ; and in his figure represents the antennae and caudal 
appendages as without setae. 
The figures given by Fabricius and Herbst represent 
their species also as possessed of five natatorial feet, and 
the antennae and caudal appendages destitute of setae. 
Lamarck, taking these as specific differences, makes 
two species. The species of Fabricius and Herbst he 
calls N. glabra, while that of Montagu and Leach he 
calls N. ciliata . In this he is followed by Bose ; but 
Leach himself, Hesmarest, and others, consider them as 
identical. 
It is evident that both Leach and Montagu have mistaken 
the true number of natatorial feet, which have more recently 
been shown by M. Edwards to be four pairs in all the known 
species of this genus. Similar mistakes are frequently 
made by the earlier observers of the minute Entomostraca; 
and when we consider the difference in the powers of the 
microscopes made use of by different observers, we can 
easily account for the discrepancies in the several figures 
with regard to the amount of pilosity in the various parts 
represented. The figures given by M. Edw r ards, for 
instance, of the species which he describes under the 
name of N. Geojfroyi , do not show much pilosity, but 
the enlarged figures of the details represent no small 
array of setae in all the organs. I have no doubt, there- 
fore, that the species described by Montagu and Leach, 
as found in England, are identical ; and it is equally 
clear that they are identical with that described and 
figured by Fabricius, and reproduced by Herbst. 
The specimens collected by Mr. Thompson, in Clifden 
