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MILLIPEDS OF FAMILY LYSIOPETALTDAE LOOIMIS 121 



Secondary crests lower and thinner than the primary crests and 

 extending from the front margin of the subsegment two-thirds or 

 three-fourths of the way to the posterior margin, although in some 

 species there is a tendency for some of the crests to extend to the 

 back margin; sides of the crests below the apex usually pitted as 

 well as reticulated; surface between both classes of crests finely 

 reticulated. 



Poriferous carinae strongly projecting, rectangular to broadly 

 rounded in outline; pore borne near the middle of the impressed 

 area which occupies only part of the lateral margin of all except the 

 hindmost segments, the rim surrounding the impression is more or 

 less thickened or inflated and with small circular pits on the sides. 



Last segment broadly truncated behind; surface with 10 to 12 

 short setae. 



Male gonopods simple, composed of two erect pieces which usually 

 are expanded near the tip and with a 2- or 3-pronge4 arm at or 

 near the apex; outer side of gonopods at base with a quadrate or 

 subtriangular plate on each side above which there is a somewhat 

 fingerlike process directed upward and forward, with long hairs at 

 the apex. 



Males with a comb of fine hairs on the under side of the last joint 

 of legs 1, 2, and 3 ; similar combs on legs 1 and 2 of the female^. 

 The males of three species have a velutinous pad on the under side 

 of the last joint of the legs beginning with the fourth pair, and 

 sometimes extending back as far as the twenty-seventh pair. 



First three pairs of male legs distinctly T-jointed, the other legs 

 more or less conspicuously 8-jointed, although in the species with 

 pad-bearing anterior legs the eighth joint may not be distinguished 

 until further back. Females with the first two pairs of legs 7- jointed, 

 the ensuing legs usually plainly 8-jointed. 



The species of this genus are separated in the following key : 



KEY TO THE SPECIES OF COLACTIS » 



1. Body almost cylindrical, not conspicuously flattened; short, not 



over 22 mm long baboquivari 



Body noticeably flattened and over 22 mm long in specimens of 



average normal size 2 



2. Body stout, 10 to 13 times as long as broad; males without a velu- 



tinous pad on under side of last joint of any of legs quadrata 



Body slenderer, 14 to 20 times as long as broad; males with a 

 velutinous pad on under side of last joint of fourth to seventh 

 legs, at least 3 



2 A species to which Prof. R. V. Chamberlin gave the name Spirostrephon utomm has tentatively been 

 assigned to this genus, but the original description offers no character by which the species can be definitely 

 separated from the species in the present key. 



