MYRIAPODA 51 



Professor Kincaid. 1 The European P. lagurus extends far north, and 

 its American relatives will probably be found in southern Alaska. 



Subclass CHILOGNATHA. 



This subclass includes all the remaining Diplopoda, with over a 

 hundred genera and many hundreds of species. There is great diver- 

 sity of form and structure, but all have the body protected by more or 

 less complete chitinized rings. 



ANALYTICAL KEY TO THE WEST AMERICAN ORDERS OF 

 CHILOGNATHA. 



Body composed of 20 (rarely 19) segments, which are complete 



chitinous rings, without sutures Order MEROCHETA. 



Body composed of 30 (rarely 26 or 28) segments or more ; fusion 

 of primitive sclerites not complete, at least the pedigerous lamina 

 separated by distinct sutures. 



Males with eight pairs of normal legs in front of the 4 5-jointed 

 gonapods* which are the posterior pair of the seventh segment 

 and the anterior pair of the eighth ; head and mouth parts partly 

 reduced, the latter suctorial rather than manducatory. 



Order COLOBOGNATHA. 



Males with seven more or less normal legs in front of the seventh 

 segment, of which the anterior, and usually both pairs, are 

 transformed into simple or 2-jointed gonapods ; head large, the 

 mouth parts well developed and distinctly manducatory. 

 Segments 1-5 with a single pair of legs each ; pleurae indicated by 

 a longitudinal suture, which is met above by two transverse 

 sutures crossing the dorsal part of the segment ; labrum with a 



median sinus Order ANOCHETA. 



Segment 3 or segment 4 footless, segment 5 with two pairs of 

 legs ; pleura? entirely obliterated ; transverse suture single or 

 wanting ; labrum with a median tooth. 

 Pedigerous laminae free ; last segment with spinning organs in 



the form of setiferous papillaj Order CCELOCHETA. 



Pedigerous laminae adnate; last segment without setiferous 

 papillae Order ZYGOCHETA. 



1 Polyxenus pugctensis, Entomological News, ix, p. 192, 1898. This form was 

 also collected by Professor Kincaid at Metlakatla, Alaska, while with the Harri- 

 man Expedition. 



2 This term is used in the present paper as a substitute for ' copulatory legs,' 

 In accordance with the excellent suggestion of the German zoologist Dr. C. 

 Verhoeff. 



