322 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
imt.pl. interambulacral plates. p.ven.a. posterior ventral arms. 
l.b.w.v. lat. branch water vessel. rad. radii. 
lig. ligaments. rad.pl. radial plates. 
in. lateral nerve. rad.ep.c. radial epineural canal. 
l.t.f. cavity of tube-foot. rec. rectum. 
mad. madreporite. r.n. radial nerve. 
mad.anvp. ampulla of ditto. r.p.h.c. rad. pseudhemal canal. 
mes.c. mesenchyme cells, rot. rotule. 
m.f.l. rauscular layer. 7.w.v. radial water vessel. 
m.g. muscular coat of gland. seg.cav. segmentation cavity. 
mo. mouth. st. siphon. 
mv.p. pores of madreporite. sk.r. skeletal rods. 
m.r. muscles of radii. sph. calcareous sphere of 
nf. nerve fibres. spheeridium. 
n.ph. nerve to pharynx. sup.s. Sup. intestinal spiral. 
@. cesophagus, sut. suture. 
op.m.t. opening muscles. t. test. 
per. peristome. to. teeth. . 
ph. pharynx. t.f. tube-foot. 
po. ambulacral pores 
t.f'. buccal tube-feet. 
pp. periproct. t.t. terminal tentacle. 
.pl. peristomial plate. 
t.c. tactile cushion. 
pp.n.7. peripharyngeal nerve.  v.v. ventral vessel. 
P.v. polian vesicles. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
or ye Po 
w.t. madreporic tube. 
PLATE 1, 
The apical system of plates. x 4. 
One of the ten peristomial plates. » 10. 
Two plates from an ambulacrum. X 4. 
A single plate from an interambulacrum. X 4. 
A bihamate spicule from the connective tissue 
layer of a tube-foot.  X 150. 
A cribriform plate from the connective tissue 
layer of an external gill. Xx 80. 
The mouth, peristome, and external gills. X 2, 
a 
