6o STALK-EYED CRUSTACEA 



b. Basal joint of external antennae without a spine at 

 its distal extremity. 



b^. Praeocular spine present. 



b^. Spines of rostrum lamellate at base, 

 acute distally. Basal ioint of external an- 

 tennas narrow. — (Scj'ra.) 



c^. Spines of rostrum flattened, contiguous, and pro- 

 duced at their extremities into a lateral lobe. Basal joint 

 of external antennae much en]arge6.-^(Ltssa.) 



c^. Praeocular spine absent. 



d'^. Rostrum elongated, its spines contiguous to within 

 a very short distance of their extremities, which are 

 acute. — {Sphenocarcinus^) 



c. Basal joint of external antennas often very much 

 enlarged, with one or more spines at its distal extremity. 



d^. Carapace subtriangular, not deflexed in front. 



e'-. Spine at antero-external angle of external antennal 

 joint very short, not visible from above. — {Pericera.) 



f'^. Spine at antero-external angle of external antennal 

 joint very long, visible from above. 



f^. Branchial spine small. Horns of rostrum more 

 or less divergent. — {Alicrophrys.) 



g^. Branchial spine large. Horns of rostrum parallel. 

 — {Macrocwlonia. ) 



A. Rostruui eviargiiiate at apex : — 



I. Libinia. 



Libinia . Leach, Say, Latreille, H. Milne Edwards, 

 De Haan, Dana, Miers. 



The carapace very convex above, in general almost 

 circular, and its dorsal surface is covered with numerous 

 tubercles, which are sometimes developed as spines. The 



