AET.18 NEW GENEEA OF MILLIPEDS — COOK AND LOOMIS 5 



trast with other long-bodied millipeds. But a few of the genera 

 are rather short-bodied, and the broad lateral expansions, or carinae 

 of the segments, are similar to those of some members of the order 

 Merocheta. 



The skeleton is weakly chitinized and the segmental sclerites are 

 distinct or not so much fused as in most of the other orders. In 

 all of the Colobognatha the pedigerous laminae are free and the 

 pleurae also may be free from the tergites or united by a lateral 

 suture. A median suture appears in one of the suborders and is 

 doubtless to be considered as a primitive character. Median sutures 

 are found in several other orders, notably the Monocheta, Merocheta, 

 and Anocheta, suggesting a fusion of two primitive sclerites to form 

 the dorsal scutes of millipeds. 



The Colobognatha differ from all other millipeds in having eight 

 pairs of normally formed legs in front of the two pairs of specialized 

 copulatory legs of the males. Also the copulatory legs, or gonopods, 

 are much less specialized than in other orders and have the joints 

 and claws distinct, as in the ambulatory legs. The posterior pair 

 of gonopods is the more specialized and does not have the same 

 position as the more specialized gonopods in the other orders, which 

 are located on the seventh segment of the body. Where only one 

 pair of legs is modified for copulatory purposes, as in the order 

 Merocheta, they are the anterior legs of the seventh segment. In all 

 of the orders where both pairs of legs on the seventh segment are 

 modified, the specialization of the anterior pair is always much 

 greater than that of the posterior pair. 



But in the Colobognatha the more specialized posterior gonopods 

 have been developed from the anterior pair of legs, not of the seventh 

 segment, but of the eighth segment, where no similar modification 

 occurs in any of the other orders. With this positional difference 

 added to the structural differences, it is plain that the gonopods of 

 the Colobognatha are not really homologous with those of the other 

 orders of millipeds, but go back as a separate line of development 

 to a remote ancestral stage when the appendages and segments of 

 the body were unspecialized. 



The different position of the gonopods affords an explanation of 

 the fact that the Colobognatha have eight pairs of legs in front of 

 the gonopods while other orders have only seven pairs. Before the 

 different attachment of the gonopods was recognized it was cus- 

 tomary to describe the Colobognatha as having an additional pair 

 of legs on some of the anterior segments which in other orders are 

 footless or are provided with only one pair. Some orders have no 

 legs on segment 3 and some have two pairs of legs on segment 5, 

 but in the Colobognatha each of the first 5 segments has a single 

 pair of legs, while the subsequent segments have 2 pairs. Thus the 



