MILLIPEDS OF MEXICO AND CENTRAL AMERICA 9 



Third segment open ventrally, the 4th and following segments closed; 

 5th segment with two pairs of legs SPIROSTREPTIDA 



Order POLYDESMIDA 



KEY TO SUBORDERS OF POLYDESMIDA 



1. Opening of sternal gonopod socket more or less constricted between 

 the gonopods, the coxae of which are entirely free of each 



other PARADOXOSOMATIDEA 



Opening of sternal gonopod socket not medially constricted; coxae 

 of gonopods connected to each other by a ligament or pseudoster- 

 nite, or else broadly in contact along the median surfaces. 



POLYDESMIDEA 



Suborder POLYDESMIDEA 



KEY TO MEXICAN AND CENTRAL AMERICAN 

 FAMILIES OF POLYDESMIDEA 



1. Body capable of being tightly rolled into a sphere or a thick, later- 



ally compressed disk 2 



Body incapable of being tightly rolled 5 



2. Pores not on the lateral keels but located high on the sides of the 



dorsum; some of the anterior keels with special flanges on inner 



or ventral side DORSOPORIDAE 



Pores, if present, always on the lateral keels; ventral surface of 

 keels without special flanges 3 



3. Surface of segments strongly hispid, irregularly roughened, tubercu- 



lar, or a combination of these; supplementary margin of segments 

 fimbriate or crenate; gonopods with large subglobose coxae par- 

 tially enclosing the distal elements C YRTODESMID AE 



Surface of segments seldom conspicuously hispid or generally great- 

 ly roughened, at most with a few broad seried tubercles; supple- 

 mentary margin unbroken or lacking; distal elements of gonopods 

 rising at or near the apex of the relatively small non-inclusive 

 coxae 4 



4. Posterior portion of segments usually sharply marked off into elon- 



gate rectangular areas; pores obviously present at or near middle 



of keels ONISCODESMIDAE 



Segments lacking posterior rectangular areas; pores absent or minute 

 and obscure, partially hidden by overlapping metazonite of preced- 

 ing segment SPH AER lODESMlDAE 



5. Segment 1 with anterior margin expanded forward over head, its mar- 



gin divided into rounded lobes, serrations, or subquadrate areas . 6 



