202 J. E. Duerden — Jamaican Actiniaria : 



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 Alphseus 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. Swiftii, are readily distinguished both externally and anatomically. 



Parazoanthus monosticlius, n. sp. 

 (PI. x., fig. 14 ; PL xiii., fig. 9.) 



The polyps give rise to extremely small colonies embedded in 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 ccenenchyme 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 ccenenchyme 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 jmrt 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. 



