REPORT ON THE PHYLLOCAEIDA. 5 



and the oral parts certainly appears very diflferent from that generally met with in the 

 other Branchiopoda, but I think it will be fully as difficult to point out any closer 

 resemblance in this respect to the Podophthalmia. The eight pairs of limbs succeeding 

 the oral parts, on the other hand, are evidently constructed on the very same type as 

 those in the Phyllopoda, agreeing, as they do, both as to structure and function with the 

 so called " branchial feet " in these Crustacea. But in Nehalia these limbs are followed 

 by four pairs of very differently formed appendages, constituting exceedingly powerful 

 natatory organs, and as similar swimming legs, the pleopoda, are also found in the 

 Podophthalmia, this character has likewise been adduced to show the decapodous nature 

 of Nehalia. It must, however, be remembered, that such organs are not restricted to the 

 Podophthalmia, but are also met with in several other Crustacea, as Amphij)oda and 

 Copepoda, and both as regards structure and number, the swimming legs in Nehalia 

 apparently agree much more closely with those in the Coj^epoda than with those in any 

 other group. This resemblance becomes still more striking by the presence in Nehalia 

 of two additional pairs of rudimentary caudal limbs, e\'idently answering to the rudi- 

 mentary legs found behind the swimming legs in several Copepoda. On the whole the 

 general appearance of Nehalia bears a very striking resemblance to that in certain free 

 living Copepoda, especially of the Harpactoid section. This similarity I do not regard 

 as merely accidental, but as indicating a true consanguinity, and this has partly also been 

 allowed by Dr. Packard. In order to understand the morphology of the PhyUocarida, it 

 thus becomes necessary not only to jsay attention to the higher Crustacea, but also to 

 the lower forms, especially the Copepoda, which seem to be the most primitive of the 

 recent Crustacea. To express shortly my opinion about the relationship of the genus 

 Nehalia, I would call it, instead of a " phyllopodiform Decapod" as it has been termed 

 by Metschnikoff, more properly a " copepodiform Branchiopod." At the end of this 

 Eeport, when the Challenger forms have been described, I propose to enter more in detail 

 into the question of the homology of the recent PhyUocarida with other known Crustacea. 

 As to the supposed affinity of the genus Nehalia to the fossil Palaeozoic forms referred 

 to the order PhyUocarida, the general appearance of the carapace, and especially the 

 presence in some of them of a similar jointed rostral plate as in Nehalia, seems in fact to 

 point to some closer relationship, but as the limbs of these old Crustacea are stUl whoUy 

 unknown, and moreover, as the taU in most of them exhibits a rather different aspect, 

 the degree of affinity must still be regarded as very doubtful. In any case these 

 Palfeozoic forms cannot be placed within the same famUy as Nehalia, but ought to be 

 separated as a distinct subdivision, and some of the forms exhibit such an anomalous 

 aspect as hardly even to justify the view that they belong to the same order. On the 

 other hand, it is cpiite evident, that the two new generic types from the ChaUenger 

 collection, described below, are on the whole so closely related to Nehalia as to ho. 

 properly classed together with this genus in the same family. 



