110 University of California Publications in Zoology ["Vol. 23 



2. Body compressed, abdomen extended, straight, no transverse suture on 

 telson ( Superf amily Thalassinidea). 



a. Abdominal pleura large. 



Axiidae, p. 110. 



b. Abdominal pleura small or absent. 



Callianassidae, p. 114. 



B. Uropods either present or absent; when present not adapted for swim- 

 ming but for holding the body in hollow objects; abdomen nearly 

 always asymmetrical (Superf amily Paguridea). 



1. Carapace firm in fore part and soft in hinder part. Eostrum much 



reduced. Uropoda present, adapted for holding body in hollow 

 objects. Abdomen soft, showing no trace of segmentation, 

 straight or twisted, some of the appendages lost, remaining ones 

 much reduced. Penultimate pair of thoracic legs much shorter 

 than those in front of them (the true hermit crabs). 



Paguridae, p. -121. 



2. Carapace firm all over, body crab-like. Eostrum spiniform or tuber- 



euliform. Uropoda wanting. Abdomen more or less firm, some- 

 times quite soft, often segmented, bent under thorax. Penulti- 

 mate pair of thoracic legs at least as well developed as those in 

 front. 



Lithodidae, p. 146. 



Family Axiidae 



Body shrimp-like. Abdomen extended, abdominal pleura large, tail-fan well 

 developed, adapted for swimming. First pair of legs chelate and subequal; second 

 pair small, chelate and equal; last three pairs simple. Antennal peduncle five- 

 jointed; antennal scale present as a movable, at times microscopic, thorn-like 

 structure between the second and third joints of the peduncle; an immovable 

 (antennal) thorn also present outside the scale on the second joint. 



Key to the California Genera op the Axiidae 



I. Eyes pale, without pigment. 



Calastacus, p. 112. 



II. Eyes pigmented. 



Axiopsis, p. 110. 



Genus Axiopsis Borradaile 



Carapace in front of cervical groove laterally compressed, forming dorsally 

 a well marked flat area or platform; without a median dorsal keel behind the 

 cervical groove, except sometimes a mere suggestion just before the posterior 

 border. Eyes well pigmented. Antennal "thorns" long or of middle size. 

 Exopodite of uropods with a suture. 



