2 U. S. NATIONAL MUSEUM BULLETIN 212 



The area covered by this checklist takes in all of North America north of 

 Mexico, and we include, in addition to native American forms, most of the 

 introduced European and subtropical millipeds, the majority of which have 

 become well established in our region. 



In the following essay we have discussed reasons for the adoption of the 

 present system of ordinal names. It might be added at this point that little 

 uniformity between family and order has obtained with respect to group- 

 name endings. In accord with what seems to be general practice in a great 

 many animal groups, we have adopted the ending "-idea" for suborder and 

 "-oidea" for superfamily. 



Studies of the phylogeny of diplopods have not yet been made which 

 would permit a "natural" arrangement of the groups. Although our se- 

 quence of orders is that used by several workers, it cannot be said to show 

 progressive specialization or any other form of evolutionary pattern. We 

 have adopted the expedient of listing families, genera, and species alpha- 

 betically, and this method certainly has its advantages in terms of con- 

 venience to the user. We venture the optimistic hope that the next listing 

 of this sort will be able to boast at least a preliminary arrangement of fami- 

 lies according to their natural relationships ! 



Ordinal nomenclature 



In the matter of nomenclature of the diplopods, there persists considerable 

 confusion, particularly with reference to the groups above the rank of 

 family, largely because the International Rules of Zoological Nomenclature 

 provide no standard for fixing the validity of names at that level. In this 

 respect few branches of systematic zoology have suffered more vicissitudes. 

 It seems desirable, therefore, to summarize here something of the history of 

 the changes in classification as they have arisen, and of several systems in 

 use by different authors and students of the Diplopoda or to be encountered 

 in the literature. 



Linnaeus in 1758 ("Systema Naturae," ed. 10) under his "Insecta Aptera," 

 placed the only two genera of myriapods recognized by him, namely Julus 

 and Scolopendra (and, curiously enough, referred the forms now called 

 Polyxenus to the latter). From the time when, in 1802-1805, Latreille 

 ("Histoire Naturelle . . . des Crustaces et des Insectes") set up his "legion" 

 Myriapoda with its two orders Chilognatha and Syngnatlia, and Leach in 

 1814 elevated the Myriapoda to the rank of a separate class coordinate with 

 Crustacea, Arachnida, and Insecta, there has continued the expansion and 

 development of a system more and more adequately representing the 

 Chilopoda and Diplopoda and their relationships. 



With Brandt (1833-1841), Gervais (1837-1847), Newport (1844), Wood 

 (1864-67), and Saussure (1872), the classification was much elaborated. 

 Brandt in 1833 proposed for the Chilognatha three subdivisions based on the 

 degree of coalescence of the visible elements of a segment, naming them 

 Pentazonia, Trizonia, and Monozonia. The first of these has maintained 



