C. L. Edwards 
295 
distally by transverse beams to form the spire and crown. At the last, from each 
corner, 3 teeth are developed, 2 horizontal diverging at right angles and the 3rtl 
perpendicular to the plane of the others. The characters of the table show 
increasing variability in the following order, arranged according to the average of 
the standard deviations in adidt and young, given after each character : — 
Number of teeth on crown (11), number of spines on disc (14), diameter of 
hole in crown (2*1), number of peripheral holes in disc (2"3), diameter of crown, 
not including teeth (2'4), diameter of crown including teeth (5"5), diameter of disc 
(5'6), and height of table (9'4). The tables in the bivium have more peripheral 
holes, spines, and teeth, broader crown, larger crown-hole and longer teeth than in 
the trivium, although the difference in some of these characters is very small. 
The average mean number of spines on the disc of the table in both bivium 
and trivium is '6 in H. floridana and "7 in H. atra while 80 7_ of the former and 
82 of the latter are without spines. Thus it is clearly apparent that the 
possession of spines is not a differential character for either species, and in connec- 
tion with the much discussed variety amboinensis of Semper is of no importance 
whatever. 
Rosettes. — Standard deviation slightly larger in the greater than in the smaller 
diameter. 
Calcareous iHng. — The pieces of the calcareous ring are more regular and 
delicate in the young. A variation of the radiale is found with notches toward 
the sides of the anterior margin. 
Polian vesicles and stone-canals. — Increase in number and length with the 
growth of the animal. 
C. Additional Characters of H. floridana. 
Growth. — The embryo during the 5th day after fertilization and still within 
the vitelline membrane is "33 mm. in length, "28 mm. in diameter and '0102 cnv' in 
volume. In the 75th day it is 4 mm. in length, "95 mm. in diameter and 1'4175 cm.'' 
in volume. 
Adopting a volume of 50 cm.-' as the limit in size of the fully developed young, 
this group averages 7 cm. in length, 2 cm. in diameter and 13 cm.^ in volume. 
The adult average 18 cm. in length, 5 cm. in diameter and 210 cm.* in volume. 
The greatest length is 33 cm., the greatest diameter 8 cm., and the greatest volume 
885 cm.3 
Tentacles. — 20 have less, and only 6 ^/.^ more, than the mode of 20. 
Developynent of tentacles. — In relation to their origin from the radial canals, the 
4 primitive tentacles of the 4th day embryo are d\, left dorsal ; d\ right ventral ; 
rl, mid-ventral and d\, left ventral (cf Scheme of Symmetry, Fig. A, PI. V). 
