J. W. Jackson, etc. — Notes on Myriopoda. 407 



dealing with a "flat-backed" millipede, 1 the dorsal plates (or 

 tergites) being furnished with definite lateral expansions. The 

 anterior part of each segment (prozonite) is almost completely 

 hidden by the segment in front. Thus little more is visible of each 

 segment than the posterior portion (metazonite). Each metazonite 

 is characterized dorsally by a definite transverse groove extending to 

 within a short distance of the lateral margin, thus dividing the 

 segment into two unequal parts, an anterior third and a posterior 

 two-thirds. Most of the segments exhibit traces of lateral spine- 

 bases ; about the width of each metazonite from its lateral border its 

 posterior portion shows definite traces of one of these lateral spine- 

 bases, but we have been unable to find any trace of other spines on 

 the tergites. This is definitely contradictory to Baldwin's inter- 

 pretation (Baldwin, op. cit., 1911, p. 76). 



Fig. 1. — Five segments from the cast of Palceosoma giganteum (Baldwin sp.) 

 seen from above, showing the undercrushing of the right side of the body 

 and exhibiting most of the essential characters of the tergites and some of 

 the more ventral features as seen through the decorticated dorsal surface. 

 Owing to decortication no left spine-bases are visible, and those of the 

 right side are not seen in this view. M, metazonite ; A^, anterior third ; 

 G, groove; Pf, posterior two-thirds; Pr, position of prozonite; B, casts 

 of leg-bases ; S, spiracles ; L, L, lateral expansions, x 1. H. K. B.-B. 

 del. 



Turning to the cast we find some twenty-six of the posterior body 

 segments represented. The anterior third of each metazonite is less 

 elevated than the posterior two-thirds. The single row of lateral 

 spine-bases is clearly visible on the right-hand side of the body. On 

 the left, portions of the dorsal surface of each segment are wanting, 

 and the underlying features are partially exposed. On this side of 

 the body, lying beneath each metazonite, there are two elongated 

 spiracle-bearing grooves nearly at right angles to the long axis of 

 the trunk; close to these and corresponding to them are the hollow 



1 Owing to the direction of the relative displacement of the dorsal and 

 ventral parts of the animal's body, it is clear that the right-hand side will be 

 more convex than in life and the left-hand side will tend to be flatter than in 

 life. It follows that when alive the animal was definitely convex dorsally 

 from side to side, but the degree of convexity can only have been slight, and 

 the animal is consequently correctly regarded as a " flat-backed " millipede. 



