364 J. E. Duekden — Jamaican Actiniaria : Parti. — Zoanthece. 



had under consideration. The dimensions, amount of the polyps not immersed in 

 ccenenchynie, and the general form of the colony well agree. I feel all the more 

 assm-ance in this seeing that similar specimens may be collected in abundance 

 from what we may regard as the original locality of the type. It is not at all 

 improbable that Sloane obtained his examples from precisely the same Cays, these 

 being, as already mentioned, the usual and most favourable spots for marine 

 collectors. 



Duchassaing and Michelotti (1860) describe as P. ocellata a form which, in their 

 later paper (1866), they place under P. mamillosa. They also regard the Corticifera 

 flava of Lesueur as a variety. It seems pretty evident that these authors, taking 

 the number of tentacles as a criterion, introduced some little confusion, so that it 

 is now very difficult, if not impossible, to ascertain what forms they are really 

 describing. 



There is nothing appearing in the original description and figure of P. cinerea 

 which is not met with in the large amount of material of P. mammillosa which has 

 come under my observation, the colour, form of the original polyps, and incrus- 

 tations of the latter presenting all the variations ascribed to the former, while the 

 number of tentacles exactly corresponds. 



The species is readily distinguished in situ from the next one by its habit of 

 growth, occurring mostly in numerous, closely associated, irregularly shaped, 

 small, high colonies, separated by channels 2 or 3 cm. across. The colonies are 

 usually from 8 to 10 cm. in diameter, but may be more. The individual polyps 

 are also larger, and appear to open more readily and constantly, and to have a 

 greater free distal portion. 



The larger number of capitular ridges, tentacles, and corresponding mesenteries 

 is evidently constant. The variations in transverse dimensions are more clearly 

 indicated in sections. In the present species the diameter is often 0*6 cm., while 

 in the next it is rarely more than - 35 cm. 



Histologically I have not been able to detect much specific difference. 

 Numbers of sections have been examined from various colonies, some with the 

 incrustations in situ and others decalcified. Although the incrustations are 

 abundant and uniformly distributed throughout the colony, the mesogloea is 

 apparently not so crowded with them as in P. caribcea. 



The basal canals appear more rounded, and perhaps the internal pigmentation 

 is not so dense in the present example ; also, as shown in the figure, the cavities 

 of the sphincter muscle are not in such a regular row. 



