CRUSTACEA. 343 



Genera Asaphus, Calymene, Bumastus, Trinucleus, Ogygia, &c. 

 (all extinct). 



Order Xiphoshra. 



Abdominal segments trilobed : limbs forcipated and lamelliform : 

 branchiae lamelliform and abdominal; a sword-shaped caudal ap- 

 pendage. 



Genus Limulus. 



Order Phyllopoda. 



Body divided into numerous segments, with lamelliform branchial 

 limbs. Eyes sometimes confluent, sometimes distinct and subpedun- 

 culate. 



Genera Branchipus, Apus, Limnadia, Artemia. 



Order Cladocera. 



Body articulated, defended by a bivalve carapace, and with mem- 

 branous lamelliform branchial limbs. Eyes, in most, confluent. 

 Genera Daphnia, Evadne. 



Order Ostrapoda. 



Body obscurely articulated, defended by a bivalve carapace, with 

 natatory limbs. Eyes confluent. 

 Genera Cypris, Lynceus. 



Order Copepoda. 



Body distinctly articulated, with many pairs of natatory limbs ; 

 females with external pendent ovisacs. 



Genera Cyclops, Cyclopsina, Anomalocera, Calayius. 



Sub-class MALACOSTRACA. 



Body divided into thorax and abdomen, with seven segments in 

 each. 



Division EDRIOPHTHALMA (with sessile eyes : no carapace). 

 Order L^modipoda. 



Abdomen rudimentary ; palp of thoracic limbs vesicular and 

 branchial. 



Genera Cyamns, Caprella, Leptomera, Aegina. 



Order Isopoda. 

 Abdomen normal, with branchial limbs : thoracic limbs subequal, 

 uncinated, with basal marsupial plates in the female. 



Genera Cymothoa, Sphceroma, Idotea, Asellus, Oniscus, Bopyrus, 



z 4 



