REPORT ON THE PHYLLOCARIDA. 5 



aud the oral parts certainly appears very different 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 Nchalia these limbs are followed 

 by four pairs of very differently formed aj)pendages, 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 l^oth as regards structure and number, the swimming legs in Nehalia 

 apparently agree much more closely with those in the Cojoepoda 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, evidently 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 Phyllocarida, it 

 thus becomes necessary not only to pay 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 

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

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

 As to the supj)osed affinity of the genus Nehalia to the fossil Palasozoic forms referred 

 to the order Phyllocarida, 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 still wholly 

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

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

 Palaeozoic forms cannot be placed within the same family 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 quite evident, that the two new generic types from the Challenger 

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

 properly classed together with this genus in the same family. 



