400 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 113 
specific and generic criteria. This tendency is particularly evident 
in the work of R. V. Chamberlin, whose systematic outlook has been 
more or less dominated by the consideration of plectrotaxy, especially 
at the specific level. 
The approach used by all these authors might well be termed the 
classical or, better, the quantitative one because it takes into account 
the numbers of spurs on the various leg articles, as the following 
example illustrates. 
Let us consider the tenth leg of the cosmopolitan species Lithobius 
forficatus (Linné) (see fig. 1). It is clear that the prefemur, femur, 
and the tibia each bear a number of stout distal spurs. The prefemur 
bears three dorsal spurs, the femur and tibia each bear two. Ventrally 
the prefemur and femur each bear three spurs and the tibia two. The 
coxa, trochanter, and tarsus are spurless dorsally and ventrally. 
The number and articular association of these spurs has tradi- 
tionally been expressed as a fraction. The ventral spurs are then 
indicated in the position of the denominator, the dorsal spurs in the 
position of the numerator. The disposition of the spurs on each sur- 
face, dorsal and ventral, of the leg is expressed as a series of five 
figures, each of which refers to the number of spurs upon the indicated 
aoe is that of the tenth 
leg discussed above. Reading from left to right, it is easily seen that 
the first two articles (coxa and trochanter) have no spurs, that the 
prefemur dorsally has three, the femur two, and the tibia two. The 
ventral plectrotaxy is similarly determined. 
The fact that this quantitative representation is obviously con- 
venient accounts for its popularity. The formulae are readily deter- 
mined and recorded; they can be expressed in a minimum of space 
(a not unimportant advantage in these days of high printing costs); 
they convey considerable information graphically and quickly. 
Quantitative formulae, however, can tell us only how many spurs 
are borne upon the various leg articles; they fail to tell us which spurs 
are present or absent. 
leg article. For example, the formula 
Qualitative Plectrotaxy 
This considerable disadvantage was probably first fully appreciated 
by Henri Ribaut who, in 1921, published a short paper describing his 
own innovation, which takes into consideration not only the number 
of spurs present, but also the identity of those spurs as well as the 
identity of the spurs that are absent. Because his system stresses 
which particular spurs are absent and present, I have termed it 
qualitative plectrotaxy. In spite of its many obvious advantages 
the qualitative method of Ribaut was not employed by others 
