Classtjication of the Crustacea. 463 



The latter three peculiarities are to be regarded as Phyllopod 

 characters, and with them in like manner must also be classed 

 the stalked eye. 



The attempt to bring Nehalia into closer comparison with 

 one of the tliree Euphyllopod types proves to be more difficult 

 than in the case of the other groups of Crustacea. In this 

 instance the quickest way of arriving at a result will be by 

 the process of exclusion. 



A closer comparison between Esthcridaj and Nehalia, which 

 might appear to be justified on the basis of a certain similarity 

 in the shell, is soon found to be impossible. In this connexion 

 I merely recall the development of the postabdomcn and furca 

 which is characteristic of the Estheridte, where this portion of 

 the body appears ventrally flexed and terminates with claws. 

 If the Apodidaj be adduced, the shield-shaped formation of the 

 shell as well as the peculiar habit of the thoracic limbs again 

 admit of no connexion. Consequently Branchipus alone 

 remains, to which most resemblances may be pointed out. On 

 the one hand we have the development of the branches of the 

 caudal fork, which in JSehalia so greatly resemble those of 

 Branchipus, owing to their form and the fact that they bear 

 set£E along their entire margin, that the term " branchipodi- 

 form " has been applied to them by Claus *. As a further 

 point of agreement we next come to the stalked condition of 

 the eyes, as well as the shape of the thoracic limbs of Xebalia, 

 wliich bears most analogy to the foliaceous form found in 

 Branchipus, although in this respect the resemblance is much 

 smaller. These, however, are the only characters which can 

 be turned to account for the purpose of establishing a closer 

 affinity between Nebalia and Branchipus. 



In my opinion the difficulty of this comparison lies in the 

 manifold modification which is exhibited by the Branchipus 

 type when contrasted with its probable ancestors. Tiie very 

 absence of a shell gives Branchipus a greatly altered appear- 

 ance as opposed to the other types ; this condition is probably 

 to be explained as being due to the loss of a shell which was 

 originally present. This may perhaps have resembled the 

 shell of Nehalia in shape ; whether it also possessed the 

 cephalic valve (Kopfklappe) can scarcely be determined. 

 The sharp division, too, between thorax and abdomen in 

 Branchipus proves to be a secondary condition. Since the 

 number of the thoracic and abdominal segments does not agree 

 with that of those of Nehalia, in which there is similarly a 



* C. Claus, " Ueber den Organismus der Nebaliden uud die sjstemat- 

 ische Stellung der Lcptostrakeu " : Arbeiten aus deoi zoolog. lustitut zu 

 Wien, Bd. viii. 1888, p. 128. 



