130 ARTHUR DENDY. 
lanciform or hastate at one (fig. 2, c). Size variable, say 
about 0:08 by 0:004 mm. 
Triradiate Spicules.—Here again three principal varie- 
ties may be clearly recognised : 
(1) Normal sagittal triradiates ; with wide oral angle; with 
long straight shaft (or basal ray) and much shorter lateral (or 
oral) rays which may be straight or slightly curved away from 
one another (fig. 2, e). All rays rather slender, and gradually 
and sharply pointed ; orals measuring about 0°25 by 0°016 
mm. ; basal about 0°46 by0°016 mm. (The subgastral sagittal 
triradiates usually have somewhat longer and stouter rays.) 
(2) Laterally extended sagittal triradiates ; with oral rays so 
widely divergent as to be almost in the same straight line, and 
basal ray very much shorter, reduced almost to insignificance 
(fig. 2, f). Oral rays almost straight or curving slightly away 
from one another, gradually and sharply pointed, measuring 
about 0°25 by 0°012 mm.; basal ray short, straight, conical, 
about 0°05 by 0:0082 mm, but of course variable. 
(3) The “ tuning-fork”’ spicules; with all three rays long, 
straight, and slender, gradually and sharply pointed; the 
basal ray longest and stoutest, and the two oral rays running 
straight forwards, parallel to and almost touching one another, 
so that the entire spicule is much elongated in the oro-basal 
direction (fig. 2, d). The two oral rays are commonly slightly 
unequal in length. Total length of an average example, 0°74 
mm.; basal ray, 0°42 by 0°01 mm.; longest oral, 0°32 by 
0:007 mm. 
Quadriradiate Spicules.—These are exactly like the 
laterally extended sagittal triradiates, with the addition of a 
very short, straight, sharply pointed apical ray (fig. 2, g). 
In addition to the principal forms of spicules thus described, 
various intermediate as well as more or less abnormal forms 
occur, but these are neither numerous nor important. 
2. The Arrangement of the Skeleton (figs. 3—5). 
As in all the more highly organised Calcarea Heterocela, 
we can divide the entire skeleton into three principal parts, 
