448 GEOLOGICAL SURVEY OF THE TERRITORIES. 
The differential characters 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 maxille, and the very long biramous maxilla. 
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 zoéa-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- 
ne; the hinder pair in the male longer than the Ist pair. 
Bi The thorax ane its appendages clearly differentiated from an ab- 
domen. 
Internal organs —no functional shell gland; no highly developed liver 
tubes like those of all Phyllopeds; stomach and cecal 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 antenne, 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 simple reproductive 
glands. 
In short, we regard the Phyllocarida as an accelerated, prematurative 
type of Crustacea which became well established in the lowest Pri- 
Decapoda. mordial Period, flourishing at a time when 
there was no Malacostracous forms, and - 
which culminated in the Upper Silurian ~ 
Period, and became nearly extinct at the 
close of the Carboniferous. Judging the 
group by the structure of Nebalia alone, 
A . whether we consider the external or the 
ee 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, 
et save in the Carboniferous Period, no Mala- 
Copepoda. 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- 
Cirripedia. tatives were of colossal size compared with 
the living survivors. 
The accompanying diagram will express 
our views as to the relation of the Phylloca- 
rida to other Neocaridan Crustacea. 
Tetradecapoda. 
Phyllocarida. 
Nauplius. 
