MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTER1DHH. 473 
Characters of the sub-order Hydrocorallinae, and of the Families and 
Genera contained in it, modified to include the results attained by 
THE PRESENT INVESTIGATIONS. 
SUB-ORDER HYDROCOB ALLIN JE (H. N. M.) * 
Compound Idydroid stocks, growing by gemmation. Hydrophyton consisting of a 
mesh work of ramified coenosarcal canals, composed of an ectoderm and pigmented 
endoderm, lodged within channels permeating a hard calcareous support, “corallum,” 
which is deposited by the ectodermal investment of the canals, and forms masses of 
very various shape. Surface of the Hydrophyton covered with a continuous layer of 
ectoderm. Zooids of two forms, the one provided with a mouth and gastric cavity, 
“ gastrozooid,” the other mouthless and simply tentacular in function, “ dactylozooid.” 
Tentacles, when present, mostly with knobbed extremities. A well-defined muscular 
layer present in the zooids. Zooids lodged within chambers excavated in the sub- 
stance of the Hydrophyton, “ gastropores” and “ dactylopores,” lined by reflections of 
the surface layer of the ectoderm, forming the “ sacs” of the zooids. Zooids of the 
two forms either scattered irregularly over the surface of the stock, or gathered into 
groups more or less regular, in each of which a centrally-placed gastrozooid is 
surrounded by a ring of dactylozooids. Cavities of zooids communicating with coeno- 
sarcal meshwork by large canal offsets. 
I. Family Milleporidce (L. Agassiz). 
Corallum irregular in growth, arborescent or encrusting, composed of a thin super- 
ficial living layer, supported by a dead mass made up of successive preceding dead 
layers. Pores devoid of styles, divided into a series of vertically succeeding chambers 
by transverse calcareous partitions, “ tabulae.” Usually scattered irregularly, but in 
some species grouped with tolerable regularity into systems, in which a centrally- 
placed gastropore is surrounded by a ring of dactylopores. Nematocysts of two kinds 
present — the one, the three-spined form, occurring only in Hydroids ; the other ovoid 
in shape, with a thread beset with a spiral of spines. Gastrozooid s short, cylindrical, 
with from four to six tentacles with knob-like tips, set in a single whorl. Dactylo- 
zooids long, filiform, and tapering, with an irregular number of short knob-bearing 
tentacles set on at irregular intervals. Gonophores unknown, but not contained 
within special cavities in the substance of the corallum “ ampullae.” 
Genus l.t Millepora, Linnaeus (Syst. Nat., ed. 10, t. i., p. 790, 1858). — Genus with 
the characters of the family. 
* Phil. Trans. Roy. Soc., Vol. 167, pt. 1, 1877, p. 132. 
f This seems to be the sole genus which can be now included in the family. Helioporn I have shown 
to be an Alcyonarian (Phil. Trans. Roy. Soc., Vol. 166, pt. 1), and I have confirmed Prof. Veerill’s 
3 p 2 
