29 



ii. Cervical groove fine but conspicuous: the plenro- 

 branchias in advance of somite xiv, though small 

 and slender, are plumose ... ... ... Hemipenecs. 



2. The third pair of thoracic legs have an epipodite and a podo- 

 branch, the 4th pair have an epipodite : — 



i. Exopodite of the 2nd pair of maxillipeds stiff as in 

 Peneus, much longer than the endopodite : pleuro- 

 branchite small and slender but plumose ... Plesiopeneus. 



ii. Exopodite of the 2nd pair of maxillipeds slender and 

 lax, shorter even than the merns-joint of the 

 endopodite: pleurobranchia; quite large ... Arist^opsis. 



An hepatic spine : — 



1. The third pair of thoracic legs have an epipodite, but no 



podobranch, the 4th pair have no epipodite ... ... Hepojiadds. 



2. The third pair of thoracic legs have an epipodite and a podo- 



branch, the 4th pair have an epipodite : the rostrum is 



many-toothed ... ... ... ... Arist^omorpha. 



Subgenus Akist^us. 



Aristseus, Duvernoy, loc. cit. : Wood-Mason (part) loc. cit. 

 Hernipenaeus, Spence Bate (part) Challenger Crustacea Macrura, p. 299. 



Rostrum 3-toothecl, very long in the female, of moderate length in the male. 

 Cervical groove indistinct. Two spines on either side of the carapace — one 

 behind the base of the antennule, the other behind the base of the antenna : 

 no hepatic spine. 



Last 3 abdominal terga carinated, the carina in each ending in a spine. 



Terminal joint of the mandibular palp triangular. Exopodite of the 2nd 

 pair of maxillipeds slender, subcylindrical, lax, very little longer than the 

 endopodite. Dactyli of the last 2 pairs of legs setiform. 



There is no podobranch to the 3rd pair of thoracic legs, and no epipodite 

 to the fourth. The pleuro branchiae of the somites from the 8th to the 13th are 

 truly rudimentary, being either papillae or small naked filaments, or at most 

 small filaments with three or four tiny pinnules. 



The branchial formula is as follows : — 



Total 



4 + (3 ep. 



6+r. 



l + 6r. = 16+7r. + 6 ep. 



