Part I1.—Stichodactyline and Zoanthee. 193 
region, as is also the case with the two other species, rendering suitable sections 
in this region difficult to prepare. As the sponge spicules are very long in P. iono- 
stichus, much longer in fact than the thickness of the capitular wall, they are of 
necessity disposed in a regular circular series, very obvious in thick transverse 
sections (Pl. xi, fig. 9). 
The outer part of the column-wall of P. Swz/tii is loaded with inclusions, but 
none extend beyond the encircling sinus. The mesogleea there becomes extremely 
homogeneous in structure, an included cell even occurring but rarely. Such a 
strongly marked division of the mesoglcea into two parts—an outer, containing the 
inclusions, canals, cell-islets, etc., and an inner, practically homogeneous in nature 
and separated from the former by the encircling sinus—appears to be more or less 
general throughout the genus. 
The size of the colonies and the extent to which the coenenchyme is developed 
are likewise features of some importance. ‘The simplest stage is exemplified by 
P. separatus, where each polyp is distinct and surrounded by only the merest trace 
of cenenchyme. ‘To include this exceptional instance, I have slightly added to 
the previous definitions of the genus. ‘The few polyps in any colony of P. monosti- 
chus also afford but a bare indication of connecting coenenchyme ; while in a colony 
of P. tunicans or P. dichroicus, hundreds of polyps are, as it were, inserted in a 
common incrusting coenenchyme. P. Swift is somewhat intermediate in the 
dimensions attained by its colonies and the amount of ccenenchyme produced. A 
few polyps only constitute a distinct colony, each arising from a clearly separable, 
though very limited, coenenchyme. 
The species I have examined, support the experience of Haddon and Shackle- 
ton (1891, p. 623), that ‘all the members ofa single colony of dicecious Zoanthez 
belong to the same sex.” All the numerous polyps of P. Swiftii and P. tunicans 
sectionized were crowded with ova. It seems remarkable that of very many 
examples of P. separatus and P. monostichus, microscopically examined, none showed 
any trace of reproductive cells. 
Parazoanthus tunicans, n. sp. 
(JL Sy Lie, WiLs JBL Sani wile, YR IRL Seyoy sales, 2h, 6) 
Kach colony consists of a thin ecenenchyme from which numerous polyps arise 
at short distances apart, the whole completely incrusting the main stems and 
smaller branches of a large Plumularia. On the smaller branches the polyps are 
arranged in a distichous manner, in a plane at right angles to that of the pinnule 
of the Hydroid, and the polyps on the two sides are either opposite or alternate. 
On the thicker stems their distribution becomes more irregular, and the polyps 
extend all round; they often arise obliquely to the surface of the canenchyme. 
