Paleocampa, Meek and Worthen. 289 
segment in Archipolypoda. ‘This is a difference of profound 
significance, which has separated the prevailing types of 
myriopods down to the present day, lying as it does at the 
base of the distinctions between the living chilopods and 
diplopods. The discovery of this type is of the greater 
importance because we have hitherto known nothing of any 
chilopodiform myriopods previous to Tertiary times, unless 
Miunster’s dubious Geophilus proavus from the Jura possibly 
be an exception. 
In studying the Archipolypoda we necessarily confine our 
comparisons with modern types to the Diplopoda, because of 
their common possession of the fundamental feature just 
named: in the same way the comparisons between Palco- 
campa and recent forms must be reduced to the common 
features or the radical distinctions which appear in studying 
the Chilopoda. Now, although the structure of Paleocampa 
may be far less perfectly known than that of the equally 
ancient Huphoberta and its allies, enough can be seen to 
point conclusively to wide and important differences between 
it and modern Chilopoda. 
In Chilopoda, of which the modern Scolopendra or centi- 
pede is the type, the body is always depressed, formed of 
many segments, rarely as few as sixteen behind the head, 
each of which is compound, being formed of two subsegments, 
one of them atrophied and carrying no appendages; both 
dorsal and ventral plates are coriaceous, of nearly equal width, 
and possess no armature whatever excepting the simplest 
hairs, which are occasionally scattered over the surface. 
The larger subsegment bears a single pair of legs, which are 
composed of five slender, cylindrical, subequal joints beyond 
the coxa, and armed with a single apical claw; they are 
attached to the interscutal. membrane uniting the distinct 
dorsal and ventral plates of each segment, and are therefore 
separated by the entire width of the broad ventral plates. 
The hindmost legs are transformed to anal stylets, while the 
first two pair are more profoundly transformed to subsidiary 
mouth-parts, the first becoming palpi and the second stout 
nippers. ‘The head, really composed of eight primitive seg- 
ments, is apparently made up of two, each of which is gene- 
rally of about the same size as the body-segments and as 
distinctly separated ; the stout biting-jaws, composed of the 
second pair of legs, spring from this second segment of the 
head, and the palpi or first pair of legs from the hinder part 
of the first cephalic segment; the anterior part of the same 
bears the many-jointed simple antennee. 
Passing now to the comparative study of Paleocampa, we 
