CRUSTACEA OF THE PAST 263 



istic. Some of these {Pygocephalus — Fig. 83) have 

 recently been shown to possess a brood-pouch formed 

 of overlapping plates on the under-side of the thorax, 

 and thus resemble the existing Mysidacea, which 

 stand at the base of the Peracaridan series of orders. 

 Others have a pair of strong side spines near the tip 

 of the telson, and in other ways resemble the recent 



Fig. 83 — Pygocephalus cooperi, from the Coal-measures : Under- 

 Side OF A Female Specimen, showing the Overlapping 

 Plates of the Brood-pouch. (From Lankester's " Treatise on 

 Zoology," after H. Woodward.) 



Euphausiacea, so that they may have been primitive 

 members of the Eucaridan series. 



Among the Crustacea of the Carboniferous and 

 Permian epochs, there are a number of forms of 

 which the affinities were until recently quite 

 obscure. They have two -branched antennules, a 

 scale-like exopodite on the antenna, and the last 

 pair of appendages (uropods) form, with the telson, 



