54 
Rowland M. Shelley 
and should be evaluated when an analysis of the Polydesmidae 
becomes possible. 
Specific — The species groups, or major components, are natural 
entities that could be regarded as subgenera, and all three could 
conceivably have arisen from an ancestral form similar to S. inornatus, 
considered the most plesiomorphic species because of the unmodified 
distal and lateral laminae. Evolution of the toothed and prolonged 
conditions of the distal lamella from such a nondescript structure is 
easily envisioned, whereas it is difficult to imagine the reverse, 
with either of the former configurations giving rise to the other. I 
therefore consider the inornatus group as sister to the bergrothi + 
granulatus lineage. Within the bergrothi group, I am unable to re- 
solve relationships between S. insulanus, bergrothi , and simplex , which 
are shown as a trichotomy in Figure 34. Within the granulatus 
group, I consider the “normal” male tibiae and female paranota, 
and the toothed medial laminae to be synapomorphies uniting S. 
australis + virginicus as a sister clade to S. granulatus. The “nor- 
mal” male tibiae and female paranota of S. columbianus, convergent 
with these features in the Blue Ridge endemics, are also apomorphic 
for this species. No apomorphies are know for S. piger and granulatus, 
but they are supported by geographic cohesiveness as discussed by 
Shelley and Whitehead (1986) for the xystodesmid genus Sigmoria. 
I therefore believe that relationships within this line are columbianus 
+ ( piger + ( granulatus + {virginicus + australis ))) (Fig. 34). 
CONCLUSION 
As stated previously, the geographical locations of the lineages 
coupled with the ancestral phylogenetic position of S. inornatus point 
to the general area of the Cascade Mountain Range in southern 
Oregon as the primary center of evolution within the genus. A 
secondary center exists in the Blue Ridge Province, as the younger 
and possibly more successful endemic species appear to have dis- 
placed S. granulatus from these mountains and to be expanding 
into adjacent physiographic provinces. Thus, although the evidence 
in Scytonotus supports Hoffman’s contention (1969) that Appalachia, 
or in this case the Blue Ridge Province specifically, is an impor- 
tant evolutionary and dispersal center, analysis of the entire genus 
leads to the opposite conclusion regarding the relative ages of the 
eastern species. The broad occurrence of S. granulatus east of the 
Plains, including areas west of the Mississippi River, represents frag- 
mentation of an ancient range that extended west of the Continental 
Divide, and S. granulatus and piger were doubtlessly connected in 
the past. Scytonotus granulatus is thus much older than the Blue 
