LITERATURE. 



535 



separate order. In Archiulus the dorsal plates are entire, generally 

 from two to three times broader than long, and furnished with 

 a few bristle-bearing papillae. The best known species of this 

 genus have been found in the 

 Coal-measures ; but some im- 

 perfectly described Myriopods 

 from the Permian rocks of 

 Bohemia may also belong 

 here. The genus Xylobius re- 

 sembles Archiulus in general 

 features, but the segments are 

 divided by longitudinal su- 

 tures into numerous quadrate 

 sections. All the known 

 species of this genus are from 

 the Coal-measures. 



Order IV. Diplopoda 

 (Chilognatha). — This order 

 includes the recent Mille- 

 pedes, and is characterised by the fact that the body is usually 

 cylindrical, and the body-rings (except the most anterior ones) are 

 fused in pairs, each apparent segment thus coming to carry two 

 pairs of legs. The legs are small and spring from the under sur- 

 face of the segments, and each apparent ring carries a pair of 

 stigmata. There are no "foot-jaws," and the generative apertures 

 are placed anteriorly, at the base of the second or third pair of 

 legs. 



The oldest known fossil representative of the Diplopoda is a 

 form (Iulopsis cretaced) which has been described from the Creta- 

 ceous rocks of Greenland. All the other hitherto recorded fossil 

 Millepedes are of Tertiary age, the majority of the known types 

 having been found in amber. 



Fig. 440. — Xylobius Sigillaria, a Carboniferous 

 Myriopod (after Dawson), a, Natural size ; b, An- 

 terior portion, enlarged ; c, Posterior portion, en- 

 larged. 



LITERATURE. 

 Arachxida and Myriopoda. 



1. " Die Arachniden." Hahn and Koch. 1831-49. 



2. "Die Insecten und Spinnen der Yorwelt." Giebel. 1856. 



3. " On Fossil Arachnidae, including Spiders and Scorpions." Brodie. 



1882. 



4. " Die im Bernstein befindlichen Crustaceen, Myriapoden, Arachniden, 



und Apteren der Yorwelt." Koch and Berendt. 1854. 



5. "Fossil Spiders." 'Harvard University Bulletin,' vol. ii. 1882. 



Scudder. 



6. " Systematische Uebersicht der fossilen Myriopoden, Arachnoideen 



