202 J. KE. Durrpen—Jamaican Actinaria : 
in these regions. The individual polyps are closely scattered over the whole 
superficial area of the sponge, and are arranged with considerable regularity as 
regards distance apart. They are generally a little closer and less regular in the 
lower region of the sponge, where growth cannot be proceeding so rapidly as 
more distally. Numerous small pores are distributed over the sponge, and in 
most of these a commensal Alpheus was found. 
I have hesitated for some time as to whether the form can be referred to any 
of the known Antillean sponge-incrusting species. The one most likely is Zoan- 
thus parasiticus, D. & M., in which the polyps are isolated. 
This is, however, stated to be a veritable Zoanthus with fleshy walls, not 
hardened by fleshy inclusions. Under these circumstances I think it is best to 
regard the species as distinct, awaiting further discoveries to indicate the true 
nature of the Zoanthus. The Caribbean Sea is obviously very rich in examples 
of anemones commensal with sponges, but this and the next described species, 
along with P. Swift, are readily distinguished both externally and anatomically. 
Parazoanthus monostichus, n. sp. 
(Qe, Soy toler, I4b3 JE, xan, iter, Y),) 
The polyps give rise to extremely small colonies embedded im the superficial 
tissues of a dark purplish sponge, over the whole of which they are distributed 
with considerable regularity. In the retracted condition of the polyps, the 
colonies appear as minute, light-coloured catenulations, contrasting strongly 
against the dark sponge. From two to seven or eight individual polyps are 
associated in a single row, but sometimes one or two may be produced laterally, 
and so give rise to an irregularly-shaped colony. Rarely the polyps are isolated. 
An extremely narrow border of ecenenchyme surrounds each colony or individual. 
Multiplication takes place by budding, and the individuals are often so closely 
contiguous that no intervening ccenenchyme is apparent. All stages in the 
separation of one polyp from another can be observed, the coenenchyme becoming 
drawn out more and more until the constriction breaks down. In retraction the 
polyps are flattened and scarcely raised above the general surface of the sponge. 
They appear to be incapable of complete retraction; the capitulum is always 
fully visible, and a wide apical aperture remains in most, so that the mouth and 
central part of the disc are exposed. The capitular ridges are wedge-shaped, and 
number about 10. The surface is smooth, but minute, opaque white particles 
are embedded in the capitular region. 
The polyps have been observed only in the semi-retracted condition, so that 
no details of the external appearance of the tentacles and disc can be added. 
The mouth is slightly oval. 
