44 - McCMURRICH. [Vot. III. 
The disc is covered for the most part with short, stout tenta- 
cles, whose surface is elevated into a varying number of tuber- 
culiform or short, finger-like processes. They are arranged 
somewhat irregularly, and are situated principally midway be- 
tween the margin and the mouth, a circle of them, however, 
surrounding the mouth, being separated by a considerable naked 
space from the rest. The portion of the disc adjacent to the 
margin is also naked. There is no trace at the bases of the 
tentacles of any such depressions with elevated margins as occur 
in Rk. rhodostoma, but this must be regarded as a specific dis- 
tinction only, and not generic. The histological structure of the 
disc, marginal tentacles, and disc tentacles are similar through- 
out. The ectoderm (Pl. IV., Fig. 2, ec’) is thin, measuring in a 
disc tentacle, somewhat contracted, 34, on the disc near the 
margin when expanded, 27.2 u. A peculiar feature of the ecto- 
derm throughout is the entire absence of nematocysts, there 
being on the other hand numerous gland cells. The muscular 
layer is exceedingly delicate, a single row of muscle cells lining 
the smooth external surface of the mesogloea. The mesogleea, 
like the ectoderm, is very thin, measuring, in the disc tentacles, 
10.2 to 13.6 w, and in the disc, 3.4. The endoderm, however, 
presents a most remarkable appearance, differing from that of 
any Actinian I have yet studied. Its general characters are 
well shown in Pl. IV., Fig. 2, ez’. It consists of high glandular 
cells, measuring from 0.136 to 0.17 mm., and filled with a clear 
substance which does not stain, the cell walls and much com- 
pressed nuclei standing out very clearly. The cavity of the 
tentacles is filled with the secretion of these cells, which is 
apparently a perfectly homogeneous coagulable fluid. Numer- 
ous “yellow cells” are imbedded in the contents of the cells, 
especially towards their proximal ends. 
The mouth is large and almost circular, and is elevated con- 
siderably above the surface of the disc. The stomodzum is 
raised into strong folds,as may be seen from PI. IV., Fig. 3. 
The gonidia are not at all well marked ; in fact, it is not possible 
to distinguish them. 
The mesenteries, like the other regions of the body, have 
the muscular layers very weakly developed, the longitudinal 
foldings of the mesogloea, so characteristic in other species, 
being almost undeveloped and represented only by very slight 
