64 COOK 



in having one pair instead of two on segment 5. From the Colobog- 

 natha they are distinct in the cylindrical body, with completely hardened 

 segmental rings, in having the mouth-parts well developed and adapted 

 for chewing, and in having the anterior pair of legs of segment 7 modi- 

 fled into gonapods, instead of having eight normal legs in front of the 

 gonapods, as in the Colobognatha. 



The large cylindrical Myriapods so common in tropical countries 

 belong to two distinct series formerly treated as constituting two colos- 

 sal related genera, Spirobolus and Spirostreptus, but now recognized 

 as having little in common, and assigned to the separate orders, Ano- 

 cheta and Diplocheta. Only the former extends into temperate re- 

 gions, and this only in North America and eastern Asia. And since 

 the Chinese Anocheta are very similar to those of temperate North 

 America, and may have been derived from them, the absence of tem- 

 perate Anocheta from other parts of the Old World, and the relatively 

 great abundance and diversity of the Anocheta of the American trop- 

 ics in comparison with those of the Old World, may be taken as indi- 

 cations of an American origin for the order as a whole, though its 

 cosmopolitan distribution must have been attained at a very remote 



period. 



Family SPIROBOLID^. 



The Anocheta are not separated into families, but there are numer- 

 ous genera, and those of temperate North America are distinct from 

 the tropical genus Spirobolus, in which they have thus far been in- 

 cluded. 



ANALYTICAL KEY TO THE NORTH AMERICAN GENERA OF 

 SPIROBOLID^E. 



Anal valves strongly inflated and evenly convex, the margins not 

 prominent ; second segment not projecting below the lateral cor- 

 ners of the first ; males with claws of anterior legs as long as the 



distal joint , Genus Onychelus. 



Anal valves with prominent thickened margins ; second segment with 

 a prominent angle directed downward and forward beyond the 

 lateral corners of the first segment ; males with claws of anterior 

 legs not hypertrophied. 



Body slender, over ten times as long as broad; legs long, projecting 

 beyond the sides of the body ; anterior legs of male with third joint 

 much larger than the second, on pairs 4 to 7 strongly compressed 

 and with a thin ventral edge Genus Arctobolus.* 



1 A new genus, based on Arctobolus onondaga sp. nov. The type, collected 

 at Kirkville, Onondaga County, New York, in June, 1895, is 65 mm. long by 5.3 



