MILLIPEDS OF FAINIILY LYSIOPETALIDAE LOOMIS 99 



family distinguished by a nmch longer and slenderer body, with 

 more numerous segments. The other suborders have 30 segments 

 as the normal number, with rare exceptions 26, 28, or 32 segments, 

 while all the Lysiopetaloidea have 40 segments and upward. An- 

 other radical distinction is the presence of repugnatorial glands, 

 Avhich are highly developed in the Lysiopetaloidea but are wanting 

 in the other suborders. The external openings for the ejection of 

 the repugnatorial secretion are located on prominent lateral carinae 

 and form a continuous series beginning at segment 6. Sculpturing 

 of the segments into prominent longitudinal crests also characterizes 

 the Lysiopetaloidea, especially the American members of the group. 

 A regular alternation of larger and smaller crests is found in most 

 of the American genera. In some of the Old World genera the 

 crests are less accentuated. 



SPECIALIZATIONS OF DORSAL CRESTS 



In this family the numbers and arrangements of the dorsal crests 

 are remarkably definite and constant. Generic specializations are 

 shown by differences in relative sizes of the crests rather than in 

 number or arrangement. The most primitive or least specialized 

 crests may be seen in the genus Spirostrephon^ which is distributed 

 eastward from Texas and Arkansas and has all the crests nearly 

 equal. All the genera from the Western States have larger and 

 smaller crests m regular alternation, so that it is easy to distinguish 

 at once the primary and secondary crests and to observe their dif- 

 ferences of size and arrangement. Such comparisons are facilitated 

 by noting the fact that in all the members of this family the median 

 line of the segments is marked by a fine longitudinal sulcus. On 

 each side of the median line is a small or secondary crest, then large 

 and small crests are repeated. The lateral crest or carina that bears 

 the repugnatorial pore is obviously different from the others. The 

 anterior segments have four primary dorsal crests, the other segments 

 six. 



The complete and typical number of the dorsal crests, between the 

 pore-bearing carinae, is 14. On each side of the median line are 

 three primary dorsal crests, alternating with four secondary crests, 

 or seven crests on each side. The full number of crests is found on 

 the segments at the middle of the body, and the number on these 

 segments is the same for all the members of the group. Smaller 

 numbers of dorsal crests are found on some of the anterior segments, 

 but a transition occurs to the full number of crests, which then 

 remains constant. Occasional irregularities, as suppression or dou- 

 bling of one or two crests of individual segments, are sometimes 

 found, but the pattern generally is maintained with remarkable pre- 



