The following key is proposed to distinguish the genera : \ 



1. Epistome absent; ext. maxillipeds almost in contact with the 



bases of the antennules. Rostrum prominent, pointed, 

 concave transversely. Dactyli of walking legs very long, 

 styliform, not depressed, almost wholly straight and ending 



in an acute point, with two longitudinal rows of hairs and ! 



without spines at inner side Hymenosoma Desmarest , 



Epistome present. Dactyli of walking legs with spines at ^ 



inner side 2 I 



2. Epistome rather long in longitudinal direction. Antennulae j 



and antennae almost completely concealed beneath the ] 



rostrum; the latter projecting (as also the lateral borders ' 



of the carapace), triangular, truncate or tridentate. The j 



ext. maxillipeds completely close the buccal cavern ; merus '. 



shorter than ischium 3 ' 



Epistome short in longitudinal direction. Antennulae and 



antennae only at base concealed by the rostrum, that is ! 

 triangular, trilobate or trispinose, but marked off poster- 

 iorly by a raised rim, that borders the flattened part of j 

 the carapace and is continued across the base of the j 

 rostrum. Ext. maxillipeds slightly gaping; merus somewhat 



longer than ischium. Sides of carapace with one or two ' 



(very rarely more) teeth at either side, but sometimes i 



unarmed 4 ! 



3. Rostrum elongate, triangular. Epistome very long, somewhat ; 



convex. Antennulae separated by a mere ridge . . Trigonoplax H. Milne-Edwards ! 



Rostrum short, triangular, trilobate or truncate. Epistome ; 



shorter. Antennulae separated by a more or less prominent ' 



- septum Elamena H. Milne-Edwards i 



i 



4. Rostrum consisting of three equidistant and equal, obtuse 



lobes, between the intervals of which the antennulae are ■ 



visible. Sides of carapace with two teeth on either side. 



Walking legs rather robust, not much longer than breadth \ '■ 



of carapace Halicarcinus White j 



Rostrum trilobate (the median lobe being inserted beneath ■ 



the level of the lateral ones), triangular, truncate or tri- '. 



spinose. Sides of carapace unarmed or toothed. Walking 



legs mostly very slender, spider-like, elongate, but some- j 



times short and thickly hairy 5 



5. Walking legs very thin and slender, much elongate; dactyli ' 



falciform, of nearly equal breadth till near tip. Rostrum '■ 



4 I 



