20 



I. The cervical groove cuts or breaks the post-orbital crests at a point in or near the 

 longitude of the inner limit of the external orbital tooth : — 



i. The legs are of moderate length ; in the two middle jiairs the propodite 

 is about two or two and a half times as long as broad : — 



1. Carapace either slightlj' convex or flat, its depth decidedly less 

 than half its length : — 



a. Merus of external maxillipeds broader than long . . Group I. 



b. Merus of external maxillipeds as long as broad . . Group II. 



2. Carapace strongly convex fore and aft, its depth quite half its 



length ........ Group III. 



ii. The legs are very long and slender ; in the two middle pairs the pro- 



.podite is three or four times as long as broad . . . Group IV'. 



II. The cervical groove does not distinctly cut the post-orbital crests ; but runs 



towards them, and then either becomes lost in the rugosities tliat lie between 



their outer ends and the lateral epibranchial teeth, or else may be indistinctly 



deflected behind the crests towards those teeth .... Group V. 



The following are the sponsor-species of the several groups, for the Indian 

 fauna :■ — 

 ^ > Lo Grroup I. : P. Jluviatile ibei'icum and P. atkinsonianum. 

 p i': Group II. : P. andersonianum. 

 \) ■'■]'% Group III. : P. pealianiim. 

 '^•\\\ Group IV. : P. austenianum. 



fe.H-t Group V. : P. manii (probably the P. larnaudii of some authors) and 



P. stoliczkanum. 



Group I. : ibericum and atkinsonianum group. 



In this group (which includes P. ibericum and varieties, P. atkinsonianum 

 and varieties, P. koolooense, and P. bifarium) the cervical groove is well' 

 defined and cuts the post-orbital crest on either side at a point in line with the 

 inner limit of the external orljital tooth, and the merus of the external maxil- 

 lipeds is very distinctly broader than long. 



The species of this group may be tabulated as follows : — 



I. The epigastric crests are distinctly in advance of the post-orbital crests 

 and independent of them : — 



i. The front in the adult is a third or more than a third the 



greatest breadth of the carapace . . . .P. ibericum and var. 



ii. The front in the adult is considerably less than a third the 



greatest breadth of the caraj)ace . . . .P. koolooense. 



II. The epigastric crests, though separated from the post-orbital crests by a 

 groove, merelj' form the convexity of a common curve with the latter : 

 front in the adult less than a third the greatest breadth of the 

 carapace : — 



i. Propodites of two middle pairs of legs about twice as long as 

 broad : — 



1. Size small, carajiace of adult not exceeding 1] inch in 



length . . . . . . .P. koolooense. 



2. Size large, carapace of adult \h inch or more in length . P. atkinsomtinum. 

 ii. Propodites of two middle pairs of legs more than two and a 



half times as long as broad . . . . .P. bifarium. 



