348 ARTHROPOD A. 



exclusively Palaeozoic. The genus Aspidocaris, however, is 

 allied to Discinocaris, and is found in the Triassic period. 



In Hymenocaris (fig. 203, 6) the carapace is comparatively 

 large, sub -triangular, apparently not bivalved ; there are 

 nine free abdominal segments, and the last carries three pairs 



Fig. 203. Paleozoic Phyllopods. a, Ceratiocaris papilio Upper Silurian (Salter) ; ft, 

 Hymenocaris vermicauda Upper Cambrian (Salter); c, Discinocaris Browniana, without 

 the " rostrum "Lower Silurian (Original) ; d, Peltocaris aptychoides Lower Silurian (Wood- 

 ward). 



of unequal lanceolate appendages. In Caryocaris the cara- 

 pace is bivalved, pod-shaped, and truncated behind, and the 

 last abdominal segment carries three spines. Allied to the 

 preceding, but much more important, and with a much wider 

 range in time, is the genus Ceratiocaris (fig. 203, a). In 

 this type the carapace is bivalve, hinged along the back, the 

 valves being semi-oval or pod-like in shape, contracted in 

 front, with an abrupt posterior truncation. The surface of 

 the carapace is marked with fine linear striae, and there are 

 fourteen or more body-rings, of which the last five or six 

 were free. The telson is composed of three long spinose 



