4 THE VOYAGE OF H.M.S. CHALLENGER. 



view of the late Dr. v. Willemoes Suhm in placing it among the Schizopoda. In my 

 opinion the genus Nehalia ought to be retained within the order of the Branchiopoda, 

 though representing a distinct subdivision or suborder, for which the name Phyllocarida, 

 proposed by Dr. A. Packard, as the older one, must be preferred to that proposed by 

 Professor Claus. The order Branchiopoda will thus contain the following subdivisions : — 

 Phyllocarida, Phyllopoda, Cladocera, Branchiura, the type of the last division being the 

 genus Argulus, which in my opinion cannot properly be referred to the Copepoda, as 

 proposed by Claus, but, in accordance with the views set forth by Thorell and others, 

 may find its proper place among the Branchiopoda, though it deviates still more from 

 the type of the order, the Phyllopoda, than is the case with the genus Nehalia. 



It seems to be a generally adopted assumption, that the genus Nehalia forms a 

 distinct transition between the Phyllopoda and the Podophthalmia, and that its afiinity 

 to the latter is even closer than to the former. I have been led to a rather different 

 view as to the relationship of Nehalia, and I think we shall find, on closer examination, 

 whether we consider the external or internal organisation, that this presumed affinity to 

 the Podophthalmia is in reality only very slight, and that most of the characters adduced 

 to show the decapodous nature of Nehalia do not hold good, since they are found fully 

 as pronounced either in other Branchiopoda or in certain Crustacea not at all belonging 

 to the Podophthalmian group. Thus, the stalked mobile eyes are not only met with in 

 the Podophthalmia, but also, as is well known, in a section of true Phyllopoda, the 

 Branchipodidse, and as to structure the eyes in Nehalia evidently agree much more T\-ith 

 those in the latter than in the former. The carapace in Nehalia, it is true, exhibits 

 some resemblance to that in certain Schizopoda, as Gnathophausia, in being not connected 

 with the trunk, but we must remember that this is also the case in the Phyllopoda, 

 both in Aims and in the bivalved forms, and that this character in the Branchiopoda is 

 universal, whereas in the Podophthalmia it is exceptional, only distinguishing a very 

 restricted number of forms. Besides, the carapace in Nehalia shows both in its structure 

 and especially in the presence of a distinct adductor muscle a much closer resemblance to 

 the bivalved shell in the Phyllopoda. The form of the exposed part of the body in 

 Nehalia is very unlike that met with in the Podophthalmia, whereas the resemblance in 

 this respect to certain Phyllopoda and still more to the Copepoda is unmistakable. The 

 internal organisation of Nehalia, though rather deviating from that in the Phj-Uopoda, 

 does not show any marked resemblance to that in the Podophthalmia, being much 

 more similar to that in the Amphipoda ; neither in my opinion can the development be 

 adduced as evidence of the decapodous nature of Nehalia. 



As to the several limbs, their structure is in fact highly remarkable, indicating a 

 peculiar mixture of characters found in very different groups of Crustacea, and on the 

 whole their presumed resemblance to those in the higher Crustacea may on closer exami- 

 nation turn out to be only very slight. Thus, the structure of the two pairs of antennae 



