CAULOPHACUS SCHULZEI. 59 
have seen two branches arising at different points and extending in nearly the 
same direction. 
Wilson (loc. cit.) does not mention such spicules as occurring in the specimens 
examined by him. 
In the rare transitional (adolescent) forms described above, connecting the 
oxyhexasters, etc., with the fully developed discohexasters, etc., the rays and 
branches are quite smooth along their length but crowned at the end by small 
verticils of recurved spines. By an increase in the thickness of all parts, by a 
growth of the terminal spines, and by the addition of lateral spines along the 
length of the rays and branches, these adolescent forms become adult discohex- 
asters, etc. 
The adult discohexasters, hemidiscohexasters, and discohexactines (Plate 8, 
figs. 10, 11; Plate 9, figs. 1-7, 9-13, 17-26; Plate 10, figs. 27a, 28a, 29a) have, 
including the branches, six to seventeen rays and measure 139-264 u in total 
diameter. In the large specimens D and E these spicules attain a larger size 
(diameter of largest 264 and 260 uv respectively) than in the smaller specimens B 
and C, where the largest measured were only 240 u in diameter. The basal 
thickness of the rays is 6-15 ». The total diameter, and to a certain extent also 
the basal thickness, of the rays are, as the subjoined table shows, in inverse 
proportion to the number of rays (branches). 
DISCOHEXASTERS, HEMIDISCOHEXASTERS, AND DISCOHEXACTINES:! 
Diameter of the spicules 
Number of rays Basal thickness 
and branches of the rays u 
limits average of the 
a largest three u 
6 170-264 254 7-15 
7-8 170-250 245 7-15 
9-12 140-230 238 7-15 
13-17 139-195 161 6-8 
In the large specimens D and E the discohexactines with six simple un- 
branched rays are the most frequent. In the small specimens B and C on the 
other hand the majority of these spicules are hemidiscohexasters and disco- 
hexasters with branches on one to all six rays. 
' This table is based on the measurements of the discohexasters, etc., of all the specimens examined. 
