THE CANADIAN ENTOMOLOGIST. 177 



Type. — S. bins Chamberlin. 

 Distribution. — North Central United States. 



Besides the type, other species known to belong to this group are 

 politus McNeil, niimius Chamberlin , and yanikans., sp. nov. 



Aretiotitii 

 Most of the species of the Lithobiidae known from Central America 

 and from Mexico compose a group which may be designated as the 

 Arenobini. Among other features all have the gonopods of the male, 

 although large and prominent, composed of but a single article and the 

 claw of the gonopods of the female wholly undivided , with basal spines 

 2 + 2, large and stout, and the basal article with inner sides strongly chit- 

 inized and conspicuously excavated toward base. The dorsal spines of 

 the anal legs from 1,0,3,2,1(0) lo 1,0,3,2,2; of the penult always 1,0,3.2,2 

 in the female, and either the same or 1,0,3,2,1 in the male. Excepting 

 the new genus Soiimpius, proposed for Lithobius 7nacroceros and L. 

 decodontos of Pocock, the prosternai teeth are 2 + 2 in number with the 

 ectal spine in many species stout and tooth-like. In Sotimpiiis, which will 

 not be further discussed here, the prosternai teeth number 5 + 5 or 6 + 6 

 and the ectal spines are bristle-like. 



Genus Are?iobius gen. nov. 

 Body conspicuously attenuated, cephalad with first dorsal plate 

 narrower than the third. Dorsum smooth and. shining, especially the first 

 plate and the head. Prosternai teeth 2 + 2 with in most the spines stout 

 and dentiform or more rarely these slender and brisile-like (only in Sub- 

 genus Sititiiis). Antennae short to medium, occasionally equalling half the 

 length of the body; composed mostly of from 25 to 60 articles. Coxal 

 pores uniseriate, circular or a little transversely elongate. With one 

 exception the anal legs are armed with two or three claws. Dorsal spines 

 of the anal legs 1,0,3,2,1 normally, occasionally varying in individual cases 

 to 1,0,3,2,0 or 1,0,3,1,1; dorsal spines of penult legs in females always 

 1,0,3,2,2 ; in males nearly always 1,0,3,2,1, rarely the same as in female 

 (frequently so in immature stages) With few exceptions both the anal 

 and the penult legs are conspicuously modified in the male, the tibise of 

 both bearing special lobes, furrows or bunches of hair ; more rarely with 

 the penult legs normal and with the first tarsal joint specially modified. 

 Gonopods of female with claw large, strongly curved and entire ; basal 

 spines 2 + 2, stout; first joint with distal and inner edges strongly chitinized, 

 excavated on mesal side toward base, leaving between the two a broadly 



