366 



ARTHROPODA. 



includes Oleni with only twelve body-rings, and is wholly 

 Upper Cambrian, while Olenus appears to survive in much 

 diminished numbers in the Lower Silurian. Several other 

 genera belong to this family, but the only one which needs 

 mention is Dikelloceplialus (figs. 213 and 221, li), in which 



Fig. 222. Paradoxides Micmac. Upper Cambrian. (After Dawson.) 



the most striking feature is the broad, fan-like, often spined 

 tail, with its short many-ringed axis. The facial sutures are 

 united in front of the glabella (Billings), and the transverse 

 grooves of the glabella are like those of many Oleni in join- 

 ing from side to side. The genus is Upper Cambrian, but 

 appears to occur also in the lowest Silurian deposits. 



4. CONOCEPHALID^E. This family is a convenient one to 

 retain, though it does not seem at present possible to separate 



