I I 2 CRUSTACEA EUMALACOSTRACA chap. 



foliaceous limbs of the Pliyllopods. The abdominal appendages 

 are also biramous. The heart is greatly elongated, stretching 

 through thorax and abdomen ; there are present both the anten- 

 nary excretory glands characteristic of adult Malacostraca and 

 the maxillary glands characteristic of adult Entomostraca, and 

 both the posterior and anterior livers characteristic of the two 

 Orders respectively are present. This combination of characters 

 justifies the belief that Nehalla represents a primitive form, 

 standing to some extent in an intermediate position between 

 Entomostraca and ]\Ialacostraca, but it may be doubted if the 

 special relationship to the Phyllopoda, claimed on the strength of 

 the foliaceous appearance of the thoracic limbs, can be legitimately 

 pressed. 



Nelialia shows the clearest signs of relationship to the other 

 primitive Malacostraca, and especially to the Mysidae, which it 

 resembles not only in general form and in the essentially 

 biramous character of its appendages, but also in many embryo- 

 logical points and in the similarity in development of the brood- 

 pouch.^ 



A large number of very ancient palaeozoic fossils are known 

 which are placed provisionally with Nebcdia in the Division 

 Phyllocarida, and some of these are no doubt closely related to 

 the existing isolated genus. Hymenocaris from the Cambrian. 



SEPJES 2. EUMALACOSTEACA. 



Before entering on a description of the members of this 

 Series it is necessary to introduce and justify a new scheme of 

 classification which has been proposed by Dr. W. T. Caiman. 

 This scheme necessitates the abandonment of the old Order 

 Schizopoda, and also ignores the distinction which used to be 

 considered fundamental between the sessile - eyed Crustacea 

 (Edriophtlialmata) and the stalk-eyed forms (Podophthalmata). 



The old group of Schizopoda, to which Nebalia and the isolated 

 form Anaspidcs, to be considered later, are undoubtedly related, 

 represent very clearly the stem -forms from which the various 

 branches of the Malacostracan stock diverge. No doubt they 

 are themselves specialised in many directions, since they are a 

 dominant group in present day seas, but their organisation is 



' RobiiLson, Quart. J. Micr. &■». 1., 1906, p. 383. 



