124 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 
The oldest chilopods are species described by Scudder (Mem. Boston Soc. Nat. Hist., 
vol. 4, 1890, p. 417, pi. 38) from the Pennsylvania!! at Mazon Creek, Grundy County, Illinois. 
Only one of these, Latzclia primordialis Scudder (pi. 38 fig. 3), is at all well preserved; 
This little animal, less than an inch long, had a depressed body, with a median carina, exceed- 
ingly long slender legs, and about nineteen segments. The head is very nearly obliterated. 
Diplopoda. 
The diplopods, especially the polydesmids with their lateral outgrowths, often have a 
general appearance somewhat like that of a trilobite, but on closer examination few like- 
nesses are seen. The most striking single feature of the group, the possession by each seg- 
ment of two pairs of appendages, is not in any way foreshadowed in the trilobites, none 
of which shows any tendency toward a fusion of pairs of adjacent segments. The anten- 
nules are short, antennae absent, mandibles and maxillulce much modified, the latter possibly 
biramous, and the maxillae absent. The trunk appendages are very similar to those of chi- 
lopods, and could readily be derived from the endopodites of trilobites. 
The oldest diplopods are found in the Silurian (Ludlow) and Devonian (Lower Old 
Red) of Scotland, and three species belonging to two genera are known. The oldest is 
Archidesmus loganensis Peach (1889, p. 123, pi. 4, fig. 4), and the Devonian species are 
Archidesmus macnicoli Peach and Kampecaris forfarensis Page (Peach 1882, p. 182, pi. 2, 
fig. 2, 2a, and p. 179, pi. 2, figs. i-ig). All of these species show lateral expansions like 
the recent Polydesmidae, and these of course suggest the pleural lobes of trilobites. All 
three of the species are simpler than any modern diplopod, for there is only a single pair 
of appendages on each segment. No foramina rcpugnatoria were observed, and the eyes of 
Kampecaris forfarensis as described are singularly like those of a phacopid. 
Peach says: "The eye itself is made up of numerous facets which are arranged in 
oblique rows, the posterior end of each row being inclined downwards and outwards, the 
facets being so numerous and so close together that the eye simulates a compound one." There 
is also a protecting ridge which somewhat resembles a palpebral lobe (1882, pi. 7, fig. ia). 
Peach comments on the strength of the test, and from his description it appears that it must 
have been preserved in the same manner as the test of trilobites. It was punctate, and gran- 
ules and spines were also present. The presence of the lateral outgrowths in these ancient 
specimens would seem to indicate that they are primitive features, and may have been in- 
herited. While possibly not homologous with the pleural extensions of trilobites, they may 
be vestiges of these structures. 
The limbs are made up of seven segments which are circular in section and expand at 
the distal end. The distal one bears one or two minute spines. They are most readily com- 
pared with the endopodites of Isotelus. The resemblance is, in fact, rather close. The 
sternal plates are wider and the limbs of opposite sides further apart than in modern diplo- 
pods. Except for one pair of antenna;, no cephalic appendages are preserved. 
While these specimens do not serve to connect the Diplopoda with the Trilobita, they 
do show that most of the specializations of the former originated since Lower Devonian 
times, and lead one to suspect that the derivation from marine ancestors took place very early, 
perhaps in the Cambrian. If no very close connection with the trilobites is indicated, there 
is also nothing to show that the diplopods could not have been derived from that group. 
