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 

 paii's 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 Tabricius 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. \\\ this he is followed by Bosc ; but 

 Leach himself, Desmarest, 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 pau's 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 figm^s given by M. Edwards, for 

 instance, of the species which he describes under the 

 name of ,N. Geoff royi, 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 Eabricius, and reproduced by Herbst. 



The specimens collected by Mr. Thompson, in Clifden 



