THE PHYLLOCARIDA. 7 



uncertain and delusive guide. But in the absence of any evidence to the contrary- 

 there is every reason to suppose that the appendages of the head, thorax, and 

 abdomen were on the type of Nebalia, since there is such a close correspondence 

 in the form of the carapace, rostrum, and abdomen. But whatever may be the 

 differences between the fossil forms represented by Geratiocaris, &c., they certainly 

 seem to approach Nebalia much nearer than any other known type of Crustacea ; 

 they do not belong to the Decapoda ; they present a vague and general resemblance 

 to the zoea or larva of the Decapods, but no zoea has a telson, though one is 

 developed in a postzoeal stage ; they do not belong to any other Malacostracous 

 type, nor do they belong to any existing Bntomostracous type, using those terms 

 in the old sense. No naturalist or palaeontologist has referred them with certainty 

 to the Decapods or to any other Crustacean type than the Phyllopods. To this 

 type (in the opinion of Metschnikoff and Glaus, who have studied them most closely) 

 they certainly do not belong, and thus reasoning by exclusion they either belong to 

 the group of which Nebalia is a type or they are members of a lost, extinct group. 

 The natural conclusion, in the light of our present knowledge, is that they are 

 members of the group represented by the existing Nebalia." 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 adductor 

 muscle. 



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



3. The very long and large mandibular palpus, the long slender appendage of 

 the first maxilla, and the very long bi-ramous maxillge. 



4. The absence of any maxillipeds. 



6. The eight pairs of pseudo-Phyllopod thoracic feet, not adapted for walking. 

 [To these we would add — 5a. The ' telson ' long and slender, with two long 

 narrow setigerous cercopods as in the Copepoda.] 



6. The animal swimming on its back. 



7. No zoea-formed larva. 



The characters which separate it from the Phyllopods are— 



1. Carapace not hinged ; a rostrum present. 



2. Two pairs of well-developed long and large multiarticulate antennjB ; the 

 hinder pair, in the male, longer than the first pair. 



3. The thorax and its appendages clearly differentiated from the abdomen.'" 

 Nebalia has been so long regarded as the surviving representative of those 



more ancient and gigantic forms of Phtllocarida, which existed in such numbers 

 in the Cambrian and Silurian Seas, and became nearly extinct towards the close 



1 ' American Naturalist,' 1882, toI. xvi, p. 351 ; aud ' Monograph N.-Amer. Phyllopods,' &c., 

 1883, pp. 447-8. 



