288 
Holothuria atra 
In the cases determinable supporting rods are absent in appendages having 
end-plates of Types A and B and in the large majority of those having Type C, 
while they are about as often absent as present in those having Types D and E. 
In the two appendages without end-plates supporting rods are present. 
i. Conclusions and Definitions. 
While agreeing in general with the conclusions and definitions for H.floridana 
(p. 2G7), H. atra has part of the appendages with Type B end-plates, without 
suckers, and represents a more specialized stage in evolution, with the addition of 
Types D and E of end-plates in the trivium and Type E in the bivium. 
H. The Calcareous Ring-. 
The calcareous ring, including the variation of the radialia with notches, is 
similar in form to that of H.floridana but about twice as large. 
The growth in the pieces of the calcareous ring is shown in the two following 
specimens, ir>G, a small adult, and 158, a large adult: — • 
Specimen 
Radiale 
Inter-radiale 
Serial 
Volume 
Length 
Width 
Length 
Width 
Number 
cm.-' 
mm. 
mm. 
mm. 
mm. 
155 
58 
5-0 
5-0 
4-0 
2-5 
158 
497 
7-5 
6-7 
5-8 
6-0 
Selenka, 1867, p. 32G, notes that specimens fi"om the Sandwich Islands have 
i larger calcareous ring. Comparing the area of the radiale, 28 sq. mm. in the 
young adult, 155, with that of a specimen of H. floridana of nearly equal volume, 
15sq. mm. in ^.'^ (c£ p. 268), it is seen that the radiale is 87 "7o larger in H. atra. 
In the same way the inter-radiale is shown to be 67 larger. Comparing older 
adults 158 and 50 the volume of the former being 12 c.c. greater (cf p. 268), 
the radiale is found to be 108 '/^, and the inter-radiale 169 larger iu H. atra. 
I. Polian Vesicles. 
The Polian Vesicles are ciul)-shaped and in general arise from the water- 
vascular ring in two principal groups opposite the bases of the right and left 
ventral radial canals. In one case, 157, the vesicles arise from the entire extent 
of the ring-canal. 
