448 



GEOLOGICAL SURVEY OF THE TEREITOEIES. 



The differential cliaracters separating them from the Decapods or any- 

 other Malacostracous type are : 



1. The loosely- attached carapace, the two halves connected by an ad- 

 ductor muscle. 



2. The movable rostrum, loosely attached to the carapace. 



3. The very long and large mandibular palpus ; the long, slender ap- 

 pendage of the first maxillse, and the very long biramous maxillae. 



4. The absence of any maxillipedes. 



5. The 8 pairs of pseudophyllopod thoracic feet, not adapted for walk- 

 ing ; the animal swimming on its back. 



7. No zoea-formed larva. 



The differential characters from the Phyllopods are the following : 



1. Carapace not hinged ; a rostrum present. 



2. Two pairs of well-developed long and large multiarticulate anten- 

 nae; the hinder pair in the male longer than the 1st pair. 



3. Thv3 thorax and its appendages clearly differentiated from an ab- 

 domen. 



Internal organs — no functional shell gland ; no highly developed liver 

 tubes like those of all Phyllopods; stomach and ccecal appendages (liver) 

 entirely unlike those of Phyllopods. 



The nervous system is entirely unlike the Phyllopod type, and ap- 

 proaches more 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 two pairs of antennae, in the form of 

 the abdomen, and the two caudal appendages, as well as the spines on 

 the hind edge of the segment, in the well-developed palpus of the man- 

 dibles, in the absence of maxillipedes, as well as the simi)le reproductive 

 glands. 



In short, we regard the PJiyllocarida as an accelerated, prematurative 

 type of Crustacea which became well established in the lowest Pri- 

 mordial Period, flourishing at a time when 

 there w^s no Malacostracous forms, and 

 which culminated in the Upper Silurian 

 Period, and became nearly extinct at the 

 close of the Carboniferous. Judging the 

 phyiiocarida. gj-Q^p \)j ^he structurc of IsTcbalia 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 Mala- 

 costraca, or at least very few, existed, and 

 they thus anticipated the incoming of the 

 more specialized Decapods. Like many 

 other synthetic types, the fossil represen- 

 tatives were of colossal size compared with 

 the living survivors. 



The accompanying diagram will express 

 our views as to the relation of the Phylloca- 



Decapoda. 



Tetradecapoda, 



Branchiopoda. 

 (Phyllopoda). 



Copepoda. 



Cirripedia. ■ 



Nauplius. 



rida to other Neocaridan Crustacea. 



