in certain African River- Crabs. 



471 



wliicli tliey overhang slightly. Each spine curves over, so 

 tliat its distal part is more or less parallel to the surface from 

 which it springs, and the points are all directed backwards. 



Fig. 2. 



Fig". 4. 



Fig. 3. 



Fig. 2. Upper surface of coxal segments of {a) the first and (b) the second 

 walking-legs (enlarged). 



Fig. 3. Branchiostegal edge of carapace, viewed from bolow. 1 and 2, 

 lobes opposite the cox;e of the lirst and seconil pairs of walking- 

 legs respectively, bearing groups of strididaling-spiues ; c, portion 

 of the edge wliich is opposed to the bade of the cheliped and 

 which in this species has no specialized spines. 



Fig. 4. One of the branchiostt>gal stridulatiug-spines partly cut open to 

 show tiie cavity witliin, furtlier onlnrgcd. 



Fig. 5. Potamon ( VotinnDnnntcs) pofici/ui/ii, female. liranchiostegal edge 

 of carapace from below. Lettering as in fig. 3. In this species 

 stridulating-spiues are present opposite the coxa of the cheliped. 



The free edge of the branchiostcgite, immediately over the 

 spiuulose patches of the coxte, is produced downwards into 



31* 



