MILLIPEDS OF NORTH AMERICA 15 



KEY TO THE NORTH AMERICAN FAMILIES OF POLYDESMIDEA 



1. Coxae of male gonopods smaller, usually concealed inside the body and never con- 



nected firmly with the margin of the sternal aperture, capable of extrusion from 



the body 2 



Coxae of male gonopods larger, often conspicuously enlarged, and partially external, 

 usually attached to the margin of the socket and immovable 5 



2. Dorsum very strongly arched, with lateral keels nearly vertical; prozonites obliter- 



ated on ventral sides; keels of 2nd, 3rd, or 4th segments enlarged, the body modified 



for rolling into a sphere 3 



Without any of the preceding modifications 4 



3. Repugnatorial pores opening on upper surface of keels near 



the margin Cyclodesmidae (p. 15) 



Repugnatorial pores not detected; a large deep pit on each side of the tergites near 

 the anterior base of the keels Desmonidae (p. 15) 



4. Anal tergite broad, subquadrate Euryuridae (p. 55) 



Anal tergite subtriangular Eurydesmidae (p. (16) 



5. Repugnatorial pores borne upon special stalks or processes, coUum usually covering 



the head Stylodesmidae (p. 76) 



Repugnatorial pores not borne upon stalks ; collum not concealing the head 6 



6. Seminal canal of male gonopod widening into a distinct vesicle or ampulla near its 



distal extremity Polydesmidae (p. 63) 



Seminal canal not distally widened or modified as above 7 



7. Tubercules of tergites strongly developed (in our species) ; gonopods without pre- 



femoral processes Vanhoeffeniidae (p. 77) 



Tubercules weakly developed or obliterated; prefemur of gonopods with two long 

 slender processes Nearctodesmidae (p. 59) 



Family CYCLODESMIDAE Silvestri 



Cyclodesmidae Silvestri, 1894, Ann. Mus. Civ. Stor. Nat. Geneva, ser. 2, 

 vol. 14, p. 747. 



Genus ETHOCYCLUS Chamberlin and Mulaik 



Ethocyclus Chamberlin and Mulaik, 1941, Journ. New York Ent. Soc, 



vol. 49, p. 58. 

 Generotype: Ethocyclus atophus Chamberlin and Mulaik, by original 

 designation. 

 Range: Texas. 

 Species: One. 



Ethocyclus atophus Chamberlin and Mulaik 



Ethocyclus atophus Chamberlin and Mulaik, 1941, Journ. New York Ent. 



Soc., vol. 49, p. 58. 

 Type: Collection of R. V. Chamberlin. 

 Type Locality : Raven Ranch, Kerr County, Texas. 

 Range : Known only from type locality. 



Family DESMONIDAE Cook 

 Desmonidae Cook, 1898, Pros. U. S. Nat. Mus., vol. 21, p. 463. 



