( 60 ) 



Of the 28 or 29 recognised species 25 are found only in the Indo-Pacitic, 

 from the Gulf of Aden and E, coast of Africa (about 40° E.) to Funa- 

 futi Atoll (about 1780E.) ; 3 are known from the old-world shores of the 

 Atlantic, from the English Channel to the Cape of Good Hope, and i 

 seems to be restricted to the Mediterranean. 



Of the 3 Atlantic species one {D. piigilator) is also found in the Medi- 

 terranean, in the Gulf of Aden, and perhaps in Indian Seas as far east as 

 Singapore ; one {D, denticiilatus) is also found in the Gulf of Aden ; and one 

 (D. brevirostris) is by some authors considered to be identical with the wide- 

 ranging D. pH^ilator. 



So far as I can ascertain, no representative of this genus has been 

 discovered west of the Cape Verde Is. 



The species of Diogenes are often difficult to determine, partly because 

 many of them are very variable, and partly on account of the more than 

 ordinary confusion of names. The names here adopted for the common 

 species are those of Prof. Henderson, who in all matters of this sort seems 

 to me to combine patience and accuracy of research, with sobriety of judg- 

 ment, in an enviable degree. 



Key to the Indian Species of the genus Diogenes. 



1. The rostrum is a narrow lamina, with the free edge spinose, 

 at any rate distaliy :-- 



A. The carapace is longer than broad : left hand when 

 fully extended not inclined inwards: — 



i. Antennal acicle bifurcate, the inner (shorter) 

 branch reaches the base of the terminal 

 joint of the peduncle: outer surface of 

 left hand beset with conical tubercles, each 

 of which carries a wreath of short stiff 

 radiating setie ... .. D. merguieiisis. 



ii, Antennal acicle bifurcate, the inner branch 

 reaches about half-way along the penulti- 

 mate joint of the peduncle :— ■ 



a. The outer (longer) branch of the 



antennal acicle just, or barely, 

 reaches the base of the terminal 

 joint of the peduncle : outer 

 surface of left hand beset with 

 • claw-shaped spines ... D. diogenes. 



b. The outer branch of the acicle 



reaches well beyond the base of 

 the last joint of the peduncle ; 

 outer surface of left hand closely 

 and finely granulous ... D. custos, (Fabr.) 



