Q PEOCEEDINGS OF THE NATIONAL MUSEUM vol.72 



attachment of legs in the order Colobognatha is the same as the 

 order Anocheta, a large group of millipeds traditionally referred to 

 the genus Spirobolus. 



As a further consequence of the different position of the gonopods 

 in the Colobognatha, it follows that an uneven number of pairs of 

 unmodified legs will be found on the posterior part of the body, 

 behind the gonopods, supposing that each of the segments has two 

 pairs, except the last two segments, which are footless. The posterior 

 pair of segment 8 renders the number uneven. 



Pocock, writing in the Biologia Centrali Americana, reports an 

 even number of post-copulatory legs in a species of Platydesmus, and 

 on that account was unwilling to admit a different position for the 

 gonopods. While Pocock undoubtedly was a very careful observer, 

 accurate counting of the large numbers of legs on specimens of Colo- 

 bognatha is not easy. The ventral plates are not united to the pleurae 

 and the attachment of the legs to a particular segment often is diffi- 

 cult to determine. Since it is more feasible to count the legs accu- 

 rately on photographs than on the specimens, photographs are sub- 

 mitted as evidence of the actual occurrence of uneven numbers of 

 post-copulatory legs. 



In addition to accidental abnormalities of the legs, there is a further 

 possibility, as recognized by Pocock, that the last of the leg-bearing 

 segments might have only one pair. This would be another way of 

 explaining an even number of pairs behind the gonopods, but should 

 not be taken for granted without proof. 



Two suborders of Colobognatha are represented in America. In 

 the suborder Polyzonoidea the head is narrowed in front and in some 

 genera is produced into a slender beak. The mouth parts have been 

 described as suctorial rather than manductatory, though the manner 

 of feeding seems not to have been observed. The segments are convex 

 or flattened, sharply angled at the junction of the scuta with the 

 pleurae, but not produced into lateral carinae and lacking a median 

 suture. In the suborder Platydesmoidea the head is not narrowed or 

 produced, the segments have lateral carinae, and the median line of 

 the segments is marked with a distinct groove or suture. 



Three families are known to represent this order north of the 

 Mexican boundary. The Siphonophoridae have the head suddenly 

 constricted in front into a slender, sharp-pointed beak; the dorsum 

 is pilose and tuberculate but lacks an impressed median sulcus. The 

 Polyzoniidae have the dorsum without hairs, tubercles, or an im- 

 pressed median sulcus, and are lacking in flattened or projecting 

 lateral carinae but are provided with eyes. In the Andrognathidae 

 the dorsum is either hairy or tuberculate or both, and there is a 

 well-marked median sulcus, the lateral carinae are flattened or pro- 

 jecting and all of the species are without eyes. 



