1 882.] The Palaeozoic Allies of Nebalia. 949 



genera was enormous, but if we, as we seem to be warranted in 

 doing, regard Nebalia as a survivor and decrepid or old-age type 

 of the order, which has lost the ornamentation of the integument, 

 the size and the telson even being dwarfed, smooth-skinned, and 

 in general very simple compared with the forms which existed at 

 the time when the type culminated and before it began to die out, 

 we may have an explanation of the greater simplicity of the car- 

 apace and abdomen of Mebalia, as compared with its Palaeozoic 



From our total lack of any knowledge of the nature of the 

 limbs of the fossil Phyllocarida, we have to be guided solely by 

 analogy, often an uncertain and delusive guide. But in the ab- 

 sence of any evidence to the contrary, 2 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 corres- 

 pondence in the form of the carapace, rostrum and abdomen. 



But whatever may be the differences between the fossil forms 

 represented by Ceratiocaris, etc., they certainly seem to approach 

 Nebalia much nearer than any other known type of Crustacea ; 

 they do not belong to the Decapods; 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 Entomostracous type, using those 

 terms in the old sense. No naturalist or palaeontologist has re- 

 ferred them with certainty to the Decapods, or to any other Crusta- 

 cean type than the Phyllopods. To this type (in the opinion of 

 Metschnikoff and Claus, who have studied them most closely) 



under high powers. This structure maybe comparable with that of Dictyocaris, espe- 

 surface of the carapace is marked with hexagonal reticulations one-thirtieth of a 





ture of the limbs; for example. Sailer figures, ii 



i the Annals an* 



'»-*/ llhtory, 3d series. Vol. v, i860, p. 154, 1 



Mg. y, what he calls the 



Ceratiocaris papilio, but the figure appears to us 







esented the tergal portion c 



segments lying under the carapace. If fresh atl 





e 0' of the nature of the limbs, success might res 





