Classijicatwn of ihe Decapod Crustaceans. 475 



Key to the Families of the Astacura. 



I. Podobranchs not united with the ma-stigo- 



branchs. Last tlioracic segment fixed. 



[Sexual appendages in male. Four pleuro- 



brancha.] Nephropsidae. 



II. Podobranchs united with the mastigobranchs. 



La^t thoracic segment free. 



1. Gills have a lamina, but no hooks at the 



end of the filaments. Sexual appendagt'S 



in male. One pleurobranch or none .... Potamobiidae. 



2. Gills have no lamina, but hooks at the end 



of the filaments. No sexual appendages 



in male. Generally four pie urobranchs. . Parastacidae. 



Kei/ to the SuperfamiUes of the Anoinura. 



I. Second to fourth legs with last joint curved 



and flattened. First pair styliform or sub- 

 chelate. [Tail-fin not ad.ipted for swim- 

 ming. Abdomen bent under thorax. Ros- 

 trum small or wanting. Third maxillipeds 



have no mastigobranchs.] Hippidea. 



II. Second to fourth legs with last joint not 

 curved and flattened. First pair not styli- 

 form, rarely subchelate. 



1. Sixth abdominal limbs adapted for swim- 



ming (except in Thalassina, where they 

 are styliform). Pleura usually well deve- 

 loped. Abdomen symmetrical, 

 i. Body depressed. Pleurobranchs to host 

 legs. Often a transverse suture on 

 telson. Abdomen more or less bent . . Gal.\theidf.a. 

 ii. Body compressed. No pleurobranch to 

 last leg. No transverse sutm-e on telson. 

 Abdomen straight Thalassintdka. 



2. Sixth abdominal limbs, when present, with 



branches neither broad nor styliform, but 

 adapted for holding the body into hollow 

 objects. Pleura very rare. Abdomen 

 nearly always asymmetrical, and either 

 soft and twisted or bent under the thorax. Paguridea. 



Key to the Families of the Hippidea. 



I. First legs subchelate. Carapace flattened, 

 without wings to cover the legs. Third 

 maxillipeds narrow, with exopodites Albvineidae. 



II. First legs simple. Carapace subcylindrical, 



with wings which cover the legs. Third 

 maxillipeds broad, without exopodites .... Hippidae. 



Key to the Families of the GalatlieiJea, 

 I. Trichobranchiate. Eight arthrobranchs. No 

 limbs on second abdominal segment of male. 

 [Abdomen not folded against thorax. Second 

 antennae with 5-jointed stalk, but no scale.] JEgleidae. 



33* 



