144 



S. H. SCUDDER ON SPINED MYRIAPODS 



two such ventral plates, each bearing a pair of legs, to every dorsal plate (with the excep- 

 tion of a few segments at the extremities of the body). The Diplopoda are universally 

 considered the lower of the two in their organization and it is therefore not surprising to 

 find that no Chilopoda have been found in rocks older than the tertiary series, while nrj-ria- 

 pods with two pairs of legs corresponding to each dorsal plate range back through the 

 entire series of rocks to the coal measures. 



This being the case, in any comparison which we may make between the ancient and mod- 

 ern types we may leave the Chilopoda entirely out of account, and confine our attention 

 to the points of distinction between the ancient types and the modern Diplopoda. At first 

 we shall confine ourselves, in speaking of the ancient forms, to the large-spined species 

 alone, many of which attain a gigantic size. The head and its appendages, wherein are 

 found the greatest divergencies of structure in the different modern forms, are again so 



poorly preserved in the carboniferous species that our 

 comparisons must be drawn almost entirely from the 

 structure of the body segments, which are mainly a 

 repetition one of another throughout the body. 



In modern Diplopoda, each of the segments of the 

 body is composed in large part, almost entirely, of a 

 dorsal plate forming a nearly complete ring, for it 

 encircles nine-tenths of the body as a general rule, 

 leaving scanty room for the pair of ventral plates (see 

 Fig. 1). On the side of the body (Fig. 2) it is perfo- 

 rated by a minute foramen, the opening of an odorif- 

 erous gland; usually the ring is nearly circular, but 

 occasionally the body is considerably flattened and the 

 sides are sometimes expanded into flattened lam- 

 inae, with a smooth or serrate margin ; a few spe- 

 cies are provided with minute hairs, sometimes 

 perched on little papillae ; and the surface of the 

 body, ordinarily smooth or at best wrinkled, is 

 occasionally beset with roughened tubercles which 

 may even form jagged projections. So far as I 

 am aware, no nearer approach to spines occurs on 

 this dorsal plate than the serrate edges of the 

 lateral laminae, the roughened tubercles or the 

 papilla-mounted hairs. In the ancient forms from 

 the coal measures we find a very different condi- 

 tion of things. The body segments may be nearly 

 circular, or they may be laterally compressed, or, 

 as in many modern types, depressed ; but in all, 

 the dorsal plate occupies at most apparently only 

 two-thirds of the circuit of the body, being met 

 by broad ventral plates (see Figs. 3, 4). This 



Fig. 1. Cross section of Fig. 2. Side 



a modern Diplopod. The view of a seg- 



lines inside the ring mark ment of a mod- 



the separation of the dorsal ern Diplopod. 

 and ventral plates. 



Fig. 3. Cross section of a car- 

 boniferous Archipolypod. The 

 lines inside the ring mark the sep- 

 aration of the dorsal and ventral 

 plates. 



Fig. 4. Side 

 view of a seg- 

 ment of a car- 

 boniferous Ar- 

 chipolypod. 



