PLECTROTAXY OF CENTIPEDES—CRABILL 403 
calculate that leg’s quantitative plectrotaxic formula. Thus for 
L. forficatus, tenth leg, dorsal, by adding letters we derive the quanti- 
tative formula 0,0,3,2,2. 
Owing to the peculiar modification of the ultimate coxa, its plec- 
trotaxy requires further clarification. Ribaut interpreted its dorsal 
spur as being homologous with an anterior spur of a more anterior leg; 
consequently, Ribaut and Broelemann both refer to it as vaH=VCA. 
Although their homologization is undoubtedly accurate, for purely 
practical reasons it seems preferable to treat the lateral armature 
(VCA) separately and not in the same chart with the others. Cham- 
berlin and others, including myself, have followed this practice, re- 
ferring to these special spurs merely as “lateral spurs’ or “lateral 
armature’’. 
Discussion and Some Applications 
The great value of Ribaut’s qualitative method is that it facilitates 
analysis as well as pure description; 1t does so because it takes cog- 
nizance of the fact that the spur series of the homologous legs are 
themselves serially homologous. Studying the plectrotaxy chart for 
L. forficatus, we see that DPA occurs on every leg and that all the 
DP spurs are serially homologous because all occupy homologous 
positions on successive legs. Considering the femoral spurs, we note 
that DFA occurs on legs 1 through 10 or 11, but that it is absent on 
legs 12 through 15; this variation helps to illustrate a second important 
point. A careful study of many lithobiid forms shows that once any 
given spur makes its initial appearance upon an anterior leg, its serial 
homologues will be present without interruption (except in mon- 
strosities) upon all succeeding legs until the posterior limit of the 
series is reached. Thus, in Nadabius pullus (Bollman), DTiP makes 
its first appearance on leg 3 and reaches its posterior-most limit on 
leg 14 without interruption (see table 2). VPA does not appear 
anterior to leg 11, after which it continues uninterrupted to leg 15. 
One of my additions to the Ribaut system has been to formularize 
such information, that is, to indicate by a convenient formula those 
legs upon which any given spur series occurs. It is possible to form- 
ularize such a dispersion, as Ribaut has termed it, only because of the 
serially homologous nature of the spurs. In ZL. forficatus, DPM occurs 
on legs 1-15 and is easily and clearly represented by the formula 
DPM=1-15. Similarly, DFA occurs on legs 1-10 or 1-11 and is 
formularized by DFA=1-10, 11. To refer to any single spur without 
regard to its dispersion, we simply write, for example, DTiP(7) (DTiP 
of the seventh leg). 
A slight modification of this form of representation is useful for 
indicating the quantitative plectrotaxy of a given leg and surface 
