72 A HISTOEY OF EECENT CEUSTACEA 



and five-jointed. Mr. Miers says, ' The nearest ally to 

 Acanthocyclus is, I think, Bellia [Milne-Edwards, 1860], 

 which resembles Acanthocyclus in the more or less orbicu- 

 late carapace, in the form of the front, chelipedes, and 

 ambulatory legs, but is distinguished by the narrower, 

 more elongated merus [fourth joint] of the exterior maxil- 

 lipedes, by the broader post-abdomen [pleon] of the male, 

 and the less distinctly defined buccal cavity.' 



The legion Cyclinea, which cannot boast with certainty 

 of more than a single genus and single species, may 

 hope to have its ranks filled up in the course of time. At 

 present it does not make a very good show, even on 

 paper. 



Legion 3. Corystinea. 



The second antennas have elongate flagella. The 

 third maxillipeds usually do not make a complete closure 

 of the mouth-cavity and are extended over the anterior 

 margin of its frame. The sternal plastron is narrow. The 

 single family Corystidas does not require a separate defini- 

 tion. It does not appear to contain more than eight genera, 

 three of which are included in the fauna of Great Britain. 

 Corystes, Latreille, 1803, has a very distinguishing charac- 

 ter as compared with the forms previously discussed, in 

 that the carapace is not transverse, but much longer than 

 it is broad. Gorystes cassivelaunus (Pennant) has fre- 

 quently attracted attention by the amusing resemblance of 

 the carapace to a human countenance, which Herbst com- 

 pares to the broad-nosed Kalmuck type. It is in Great 

 Britain a convenient species for study, from the number of 

 dead specimens that are often cast up on sandy shores. 

 The sexes are easily distinguished. In the male the cheli- 

 peds are enormously elongated, and the pleon is very 

 small and has only five joints, although it is quite plain 

 that the central one of the five is in reality a compound of 

 three that have coalesced. In the female the pleon, though 

 small, is broader than in the male, and has the seven joints 

 distinct ; the openings of the vulvas can without difficulty 

 be observed on the plastron between the third pair of legs ; 



