The Paltsosoic Allies of Nebalia. 



[December, 



3. The thorax and its appendages clearly differentiated from an 

 abdomen. 



Internal Organs. — No functional shell gland ; no highly-devel- 

 oped liver tubes like those of all Phyllopods ; stomach and cce- 

 cal appendages (liver) entirely unlike those jjBpffffi^fth 

 of Phyllopods. ABSBsS^B&k 



The nervous system is entirely 1 

 the Phyllopod type, and approaches 

 the Decapod and Tetradecapod type. 



The resemblance to the Copepoda is in 

 some points quite 

 striking; this is 

 seen in the equal 

 size of the 



in the form of the 

 abdomen, and the 

 two caudal appen- 

 dages,aswellasthe 



spines on the hind FlG . ,,. _ Echinocarh 

 edge of the seg- Clevis. 

 ment, in the well-developed palpus of the 

 mandibles, in the absence of maxillipedes, 

 as well as the simple reproductive glands. 

 In short, we regard the Phyllocarida 

 as an accelerated, prematurative type of 

 Crustacea which became well established 

 in the lowest Primordial period, flourish- 

 ing at a time when there was no Mala- 

 costracous forms, and which culminated 

 in the Upper Silurian period, and became 

 nearly extinct at the close of the Car- 

 boniferous. Judging the group by the 

 structure of Nebalia alone, whether we 

 consider the external or the internal 

 structure, it is a highly composite or 

 synthetic type, combining Copepod, Phyllopod and Decapod-like 

 features with more fundamental characteristic ones of its own. 

 The group existed at a time when, save in the Carboniferous 

 period, no Malacostraca, or at least very few, existed, and they 

 thus anticipated the incoming of the more specialized Decapods. 



