C. L. Edwards 
283 
of t he doi-sal and ventral regions. The determinations for the species, recorded in 
Table XXXIV. were made from a total of 150 dorsal and 142 ventral tables. 
1. Disc. 
In the form of the disc, dorsally there are 119 (79'3 7 ,) square, 13 (S'T %) 
iiregidarly S(iuare, 13 (iS'T ' /o) rovind, 2 (l'3 7:/> irregularly round, and 3 (2 7o) 
irregular ; ventralli/, 92 (64-8 "/J square, 16 ( 11-3 / ) irregularly square, 18 (12-7 7o) 
round, 7 (4-9 /J irregularly round, 9 (6-3 /J irregular. In general, square may be 
taken as the prevailing form. 
The mean number of peripheral holes is 4, which is from 1 to 2 less than in 
H. floridana. Pearson, 1903, p. 202, notes that " the discs of the tables are smooth 
and have no peripheral perforations." The study of my series shows that Pearson's 
description cannot be held as typical for the species. 
The mean number of spines is 7 while 82 7o of the tables have discs without 
spines. In all of the characters of the disc this species agrees closely with H. flori- 
dana (cf. p. 258). 
2. Height. 
The dorsal tables are G6 /x high, 38 higher tlian the ventral, and altogether 
they are higher in H. atra than in H. floridana. 
3. Grown. 
The mean diameter, both including and not including teeth, the length of the 
teeth and the mean diameter of the hole, are slightly greater in this species than 
in H. floridana. 
The mode for the number of teeth is 12 ; the mean being slightly less dorsally 
and slightly more ventrally. 
As in the case of H. floridana, the dorsal tables have more peripheral holes, 
more spines, broader crown, larger crown- hole and longer teeth than the ventral 
tables, albeit in some characters the differences are so small as scarcely deserving 
of notice, while the number of teeth is slightly greater ventrally. 
c. Rosettes and Rosettes with Holes. 
In its simple condition the rosette has a somewhat elongated central bar with 
forked ends (PI. IV. Fig. 23). The ends fork (Fig. 24), and the branches thus 
formed grow toward one another. Later additional branches may appear at the 
middle of the central bar (Fig. 25). A large majority of tiie rosettes remain open 
as in Figs. 24 and 25, although the curved ends of contiguous branches are often 
in apposition. On some of the rosettes are little knobs, while others present slight 
irregularities of the surface which might be taken for knobs. 
When tlie distal portions of any two of these branches fuse, a hole is formed 
(Fig. 26) and such a spicule is placed in the class of rosettes with holes (Figs. 
2G— 27 f). In the bivium there are 145 (96-7 7o) rosettes and 5 (3-3 7o) rosettes 
36—2 
