6 



the eye ; its outer edge terminates in a spine, and from the proximal end of its 

 inner edoe there springs a twisted setose scale (antennular scale) which forms a 

 sort of inner wall to the orbit : the antennular flagella are cylindrical and taper- 

 ing and may be short or long, but are never as long as the body. Antenna! 

 scale large and foliaceous ; its outer edge is rigid and terminates acutely 

 antennal flagellum very long. The mandible has a jagged cutting edge and 

 a broad grinding crown : its palp (endopodite) is large and broadly foliaceous, 

 consisting of two segments of which the anterior is very much the larger. The 

 endopodite of the maxillule (1st maxilla) may be long and 2, 3, or 4 jointed, or 

 may be without segmentation and truncated : that of the true maxilla is short. 



The endopodite of the 1st maxillipeds is slender and b-jointed, that of the 

 2nd and that of the 8rd consist of 7 segments. The exopodite of the 2nd and 

 3rd maxillipeds is very well developed, being curved, compressed, stiffish, and 

 made up, like the flagella of the antennae, of numerous small joints. The 3rd 

 maxiUipeds are long and pediform. The first three pairs of legs are chelate, the 

 1st pair usually being the shortest and the 3rd pair usually the longest. The 

 last two pairs of legs are monodactylous. Exopodites are usually present on all 

 or all but the last pair of thoracic legs, but are sometimes altogether wanting. 



No podobranchise exist on any of the legs, and only one artlirohrancTi — the 

 posterior one — is present on the penultimate legs. The gills are the modified 

 pUyllobranchife known as dendrobranchige : that is to say, each gill-plume con- 

 sists of two series of plates arranged one on each side of a median stem, but 

 each plate is more or less fringed or branched. 



The abdominal appendages are of moderate length, the exopodite being 

 longer than the endopodite. In the first pair there are no endopodites, but 

 in the male their place is taken by a pair of more or less rigid, longitudinally 

 pleated and convoluted plates, known as the " petasma " or " andricum," which 

 together form a tube or canal. In the second pair the endopodite carries at its 

 base in the male a fleshy papilla. 



According to Zittel the first remains of Peneiis, as far as is known at pre- 

 sent, appear in the Lithographic slates of Bavaria {Jurassic.) 



Key to the genera included in the Peneus group. 



Indian genera are printed in capitals, 



I. Rostrum serrated on both edges : a pleurobranch on the last thoracic 



somite (XIV) : exopodites on all, or all but the last pair of the 

 thoracic legs : — 



1. First pair of chelipeds short and slender in both sexes ... Peneos. 



2. The first pair of chelipeds of the male are, typically, stouter 



and much longer than, the 2nd and 3rd pairs ... ... Heteropeneus. 



