236 A Monograj^h of Scytonotus. 



lateral larger) is such as to leave no doubt that the species 

 intended is one of a group of small North American forms with 

 20 segments, not yet separated from Polydesmns, but probably 

 more nearly related to Brachydesmus. That this latter genus 

 can be maintained solely upon the difference of one in the number 

 of segments would seem improbable, for this difference nia}^ be 

 reasonably ascribed to arrested development, and the small size 

 of the species with 19 segments gives force to the idea that the^^ 

 are depauperate forms. Nevertheless, the number of segments in 

 the adult has never been known to vary in a species, and this fact 

 gives it great importance. 



Polydesnius (Scytonotus) arcticollis Peters. 

 Monatsber. d. Akad. f. Wissensch. zu Berlin (1864), p. 539. 



This Venezuelan species is given as having 20 segments and a 

 pattern of dorsal sculpture very different from S. granulatus. 

 Peters himself afterward placed it in a new subgenus, Trachelo- 

 desmus. 



Polydesmns (Scytonotus) caesiiis Karsch, 

 Troschel, Archiv. f. Naturgesch (1881), p. 42. 



A New Zealand species, apparently having little affinity with 

 the American form, since the author says : " Segmentis alatis 

 subglabris, medio serie transversa arearum subquadratarum cir- 

 cumcisarum ornatis," 



Polydesnius (Scytonotus) woodianus Humbert et Saussure. 

 Rev. et Mag. de Zool. (1869), p. 153. 



A Mexican species with the dorsal surface wrinkled, a few 

 small flattened and scattered granules, broad, dentate carinje, no 

 elevations for the repugnatorial pores, and 20 segments. In their 

 larger work on the Myriapoda of Mexico the authors have ignored 

 Scytonotus, even as a subgenus, and referred the species back to 

 Polydesnius. That their species is congeneric with P. comjylana- 

 tus of Europe cannot be reasonabl}^ maintained, and it seems to 

 have even less affinity with Scytonotus. Neither does it seem to 



