ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
339 
Thelaceros rhizophorae.* — Mr. P. Chalmers Mitchell describes a 
new genus of Actinians obtained by Dr. Hickson in a mangrove swamp 
in Celebes. It appears to form the type of a definite family closely 
allied to the CorallimorphidaB, which may be called Thelaceridae, and 
thus defined : — Hexactiniae without a sphincter, cinclides, or acontia ; 
with numerous accessory rudimentary tentacles, so that more than one 
tentacle communicates with a radial chamber ; the normal tentacles are 
covered by small compound hollow protuberances. The accessory 
tentacles are rudimentary. The Thelaceridae appear to have protected 
themselves by a sudden vertical contraction, by which they withdrew 
themselves into the mud, and a continual selection favoured those with 
strong longitudinal muscles. The oral disc remaining uncontracted, the 
tentacles were, in correlation with this habit, peculiarly modified. The 
author calls attention to our incomplete knowledge of other Sticho- 
dactylinss, and suggests that the Discosomidae, with the abnormal 
radially arranged tentacles and unretractile disc, and the Cryptoden- 
dridae, may possibly stand on either side of the Thelaceridae. 
Anatomy of Madreporaria.t — Dr. G. H. Fowler, in commencing 
his fifth memoir on the anatomy of the Madreporaria, remarks that the 
time is hardly yet ripe for a discussion of those modifications which are 
likely to be ultimately introduced into the systematic classification by 
further morphological study. He gives, therefore, simple descriptions 
of anatomical structure, and in this memoir deals with JDuncania 
harhadensis, Madrepora sp., Galaxea esperi, Heteropsammia multilohata, 
and BatJiyactis symmetrica. Duncania is found to be a true Madre- 
porarian, and will probably be ultimately proved to be allied to such 
forms as Zaplirentis. Figures are given of the typical structure of the 
genus Madrepora. A vertical section between two polyps of G. esperi 
shows (1) the body-wall of ectoderm, mesogloea, and endoderm; (2) a 
space which is part of the common coelenteron of the colony ; (3) a layer 
of endoderm, mesogloea, and (?) calicoblasts, which directly overlies 
(4) the coenenchyme itself. 
Heteropsammia, in common with Stephanoseris and Heterocyathus, has 
a pear-shaped body; some species of all these genera are known to 
derive the curvature of the chamber from settlement on a heliciform 
shell, and it is also known that a large number of Gephyrea normally 
inhabit heliciform shells, and Dr. Fowler thinks that, in the absence of 
experimental proof, we are for the present justified in regarding the 
heliciform cavity as due, in those cases where we have no direct evidence, 
to the same cause as those in which our knowledge is more exact. The 
anatomy of the colony in the main resembles that of Hhahdopsammia 
already described by the author ; the animal is dioecious. 
Unlike the rest of the ‘ Challenger ’ material, the spirit specimens 
of BatJiyactis are histologically useless, due, possibly, to the rapidly 
diminishing pressure during their sudden ascent from the great depths 
at which these corals live. Bathyactis belongs to the imperforate 
division, and must not, therefore, be classed with the Fungiidas, which 
have been shown by Bourne to be true perforate corals. 
* Quart Journ. Micr. Sci., xxx. (1890) pp. 551-63 (1 pi.). 
t T. c., pp. 405-19 (1 pi.). 
2 B 2 
