( 112 ) 
from a sigmaspire by increase in size and loss of the spiral twist”. 
SCHULZE & LENDENFELD (1889, p. 28) stick to the contorted nature: 
“oewundene, eine halbe Spiralwinding bildende Nadel”. Finally the 
definition is again somewhat modified by LenprenreLD (1890, pp. 426) : 
“einfach spiralig gekriimmter oder bogenförmiger Stab.” 
The spicula belonging to this type, appear, like the sigmaspirae in 
the shape of the letter C or S, or as a bow. Here too these various 
appearances depend on the direction in which the spiculum is viewed. 
According to my conception only such forms belong to this group, 
which are contorted, not such in which rea//y the “hooks curve both 
in the same direction”. The latter are curved pedinaxons, the former’ 
are spiraxons. The axis, as a rule, has less than one, but more than 
half a revolution, which is easily proved by wax models. 
As a derivation or modification of the sigma we have 
2. Chela . 
BowERBANK has already shown (1858, p. 304— 805 ; reprinted 1864 
p. 47—48) that the chelae develop from sigmata. This observation is 
confirmed and enlarged by Ripiry & Denpy (1887, p. XX), Levinsen 
(1886 and 1894), H. W. Witson (1894), PeKELHARING & Vosmagr (1898, 
a p. 36—88). We remarked (1. e. p. 37): “not only can we confirm 
this but we can give a new strong argument in favour of it. This 
lies in the fact that the anisochelae of Esperella syrine are twisted.” 
I can add now that this twisted nature is found in isochelae as well 
as in anisochelae. Consequently we may regard both as (#-spiraxons. 
8. Diancistra. 
According to Riprry & Derpy (1886, p. XIX) the spicula, which 
BowrrBANK called “trenchant contort bihamate”, and for which they 
propose the name diancistra are “usually... more or less contort, 
the two hooks lying in two different planes’. My own observations 
confirm this statement and I bring the diancistra, therefore, likewise 
to the $-spiraxons. 
Resuming we may divide the monaxons into the following primary 
groups: 
I. Pedinarons. Monaxons the axis of which lies in a plane; 
(oxea, styles, tylostyles, etc). 
IL. Spiravons. Monaxons the axis of which is a screw helix. 
A. a-Spiravons. The axis is a line drawn on a circular cylin- 
der; the pitch is generally great, to this group 
belong : 
