422 R. I. POCOCK. 



basal segments are relatively larger tliaii in the Scolopendro- 

 morpha, but smaller than in the Litliobiomorpha, and they 

 show no progressive increase in size towards the posterior 

 end of the body, sucli as is characteristic of the members of 

 the latter order (PI. 23, figs. 16, 17). The legs of the 

 fifteenth pair differ in certain particulars from those of all 

 Ohilopods. The basal segments or coxge are of medium size, 

 freely articulated to the posterior end of the last somite, 

 without encroaching in any way upon its pleural area, and 

 like the trochanters of the two preceding pairs are armed 

 below with a long spike. The second segments or tro- 

 chanters, on the other hand, are reduced in size and com- 

 pletely fused with the proximal end of the femora, as in the 

 Scolopendromorpha. In the members of the latter order, 

 however, as well as in the Geophilomorpha, thecoxal segment 

 is indistinguishably united to the enlarged prsecoxal pleural 

 sclerite. Again in the Lithobiomorpha and Scutigeromorpha, 

 which resemble Craterostigmus in the freedom of the coxa,, 

 this segment occupies the whole of the pleural area of the 

 somite, and the trochanter remains distinct. As in all 

 Chilopoda, with the exception of some Greophilomorpha, 

 the tarsus of the fifteenth leg is bisegmented (PI. 23, figs. 

 18, 19). 



Projecting between the legs of the last pair is a sclerite, 

 formed by two valves united in the median dorsal line and 

 meeting ventrally, when closed, in a long slit representing 

 the combined genito-anal aperture. This bivalvular sclerite 

 is probably the homologue of the dorsal plate of the anal 

 somite, which in some genera of Chilopoda, e. g. vScolopendra 

 and the male of Lithobius, is of larger size than that of the 

 genital somite, and partially or wholly supersedes it. No 

 trace of skeletal plates of the genital somite or of gonopods 

 is visible externally. The latter in all probability have 

 atrophied from enclosure within the genito-anal cavity, 

 embraced by the above-described sclerite (PI. 23, figs. 5 — 

 7, ag.). 



