THE MYRIAP00A OF NORTH AMERICA. 213 



genus Polydesmus, as defined by H. De Saussure ; but, not being entirely certain tbat my 

 specimens are adults, I have refrained from indicating a new genus. 



When surface markings exist on the scuta, they are very useful in defining species. 

 The color is also a good character in some groups. Where one of these fails us the 

 other very generally assists. The form of the last scutum is sometimes distinctive. The 

 best characters, however, are those derived from the genital organs. The form, &c, of the 

 antennae and head often afford some clue. 



Genus POLYDESMUS, Latrdlle* 



Meatus laterales in scutis 5— 7— 9— 10— 12— 13— 15— 10— 17— 18— 19— positus. 

 Lateral pores situated upon the 5 — 7 — 9 — 10 — 12 — 13 — 15 — 10 — 17 — 18 — 19 — scuta. 



Polydesmus, II. De Saussure, Mem. Soe. Nat. Hist., Geneva, vol. xv, p. 292. 



Subgenus POLYDESMUS. 

 Dorsum eomplanatum. Laminae laterales magna;, horizonti ad libellam respondentes. 

 Dorsum complanate. Lateral lamina large, horizontal. 



P. setiger, sp. nov. 



P. brunneus; scutis squamis obtusis parvissimis (interduin obsoletis) ornatis; laminis lateralibus marginibus 

 acute valdissime serratis. 



Brown; scuta ornamented with very small, obtuse (sometimes obsolete) scales; lateral lamina with their 

 margins acutely and very strongly serrate. 



The head is broad, and has its anterior surface pubescent. The antennae are rather 

 long, filiform, pubescent, and strongly clavate. The first scutum is transversely oval. It 

 is narrower than the head. The surface of the scuta is covered with minute flattened 

 tubercles. On the more anterior these are quite distinct and arranged somewhat regu- 

 larly in a fourfold series. On the more posterior they become less and less distinct, so 

 that in some individuals these scuta have scarcely more than a rough appearance. Many 

 of these tubercles are seta-tipped, and on the posterior borders of the scuta they become 

 conical and acute, each with its rigid hair forming a sort of fringe. The lateral laminae 

 are broad and not widely separated. The serrations are less strongly pronounced on the 



* As Latreille was the original describer of the genus Polydesmus, of course his name must be connected with 

 it. But the genus, as here adopted, was first defined by II. De Saussure. 



