284 Holotlmria atra 
with holes, and m the trivium 130 (86-7 7o) rosettes and 20 (13 3 7o) rosettes with 
holes. 
TABLE XXXV. 
Rosettes and Rosettes witJi, Holes. 
EOSETTES 
Rosettes with Holes 
Greater 
Smaller 
Number 
Greater 
Smaller 
Diameter 
Diameter 
of 
Diameter 
Diameter 
Holes 
At 
Mean 
24-662 
17-148 
1-400 
24-000 
19-200 
+ •220 
+ -1.57 
+ -121 
+ 2-569 
+ 1 -289 
Standard Deviation ... 
3-931 
2 -803 
-400 
8-518 
4-293 
Dorsal 
+ -156 
+ -111 
+ -085 
+ 1-817 
+ -916 
Coefficient of Variation 
15-941 
16-348 
28 -.571 
35-492 
22-351 
+ -631 
+ -698 
+ 6-094 
+ 7-570 
+ 4-767 
Range of Variation . . . 
9-6_33-6 
9-6-24-0 
1—2 
19-2-33-6 
14-4—24-0 
j\Iean ... 
24-886 
17-022 
1 -350 
26-400 
18-240 
+ -279 
+ -154 
± -099 
+ -886 
+ -369 
Standard Deviation ... 
4-717 
2-597 
•654 
5-873 
2-448 
Venti'al 
+ -197 
+ -109 
+ -070 
+ -626 
+ -261 
Coefficient of Variation 
' 18-954 
15-2,'>9 
48-430 
22-247 
13-418 
+ -793 
+ -638 
+ 5-165 
+ 2-373 
+ 1-431 
Raii"e of Variation . . . 
1 
14-4—43-2 
9-6— 24-0 
1—3 
19-2—38-4 
14-4—24-0 
In their general dimensions and the increased size of the rosettes with holes 
these spicules in H. atra agree with those of //. floridana. Only 3 ° in the dorsal 
region are rosettes with holes and 13 '/o iii the ventral region. Of the 25 rosettes 
with holes found among the 300 rosettes and rosettes with holes of my statistical 
series, only two have 3 holes, four have 2 holes and 19 have 1 hole. 
The rosette with holes (perforated plate) of H. atra is often more or less similar 
to the developmental stages of the perforated plate in H. floridana. The rosettes 
nearly always show some of the arching of the branches of the bar (Figs. 24, 25), 
preliminary to the formation of the two central and the one or more distal holes 
of developmental Types a (Fig. 37) and b (Fig. 38) of H. floridana. Thus Fig. 27 a 
resembles Type a. Type h with the 4 additional distal holes, 2 at each end, is often 
clearly indicated, albeit rarely, if ever, having all the distal holes completed (Fig. 
27 b). (Cf Selenka, 1867, PI. VII. Fig. 4.) 
Occasional somewhat elongated "buttons" occur with two pairs of larger 
central holes and one distal hole at each end (27 c). In one case there is an 
incomplete button of this type but with three pairs of central holes (Fig. 27 d). 
This button is formed from Type a by the growth of a bar tlirough each central 
hole. Fig. 27 a shows such a bar projecting into the right central hole. If in a 
