166 J. E. DiJERDEN — Jamaican Actiniaria : 



The parietal mesenterial stomata are small, circular apertures, located a little 

 distance from the column-wall just below the sphincter muscle; the perioral are 

 somewhat larger. 



Gonads were restricted in one specimen to the second cycle of mesenteries. 

 Prof. M^Murrich (1889, p. 40) found that " the reproductive organs were present 

 on all the mesenteries, with the exception probably of the directives." 



This species is very abundant in the neighbourhood of the coral reefs around 

 Jamaica, wherever these have been examined, sometimes partly buried in the sand, 

 but more often attached to rocks. Isolated individuals may occur, but usually a 

 number are closely aggregated, so close, at times, as to give rise to a polygonal 

 outline of the discs, the result of mutual pressure. The associate habit and often 

 the presence of more than two gonidial grooves are no doubt indicative of reproduc- 

 tion by fission ; and Prof. M'Murrich obtained several specimens at the Bahamas 

 in various stages of division. A small, brightly -coloured Crustacean has been 

 found on one or two occasions living on the disc ; but this commensalism is 

 evidently not so constant a feature of the West Indian species as of those described 

 and figured by Mr. Saville-Kent, from the Australian Barrier Reef. Here a 

 brilliantly-coloured fish and one or two species of pi'awns are commensal with the 

 pol^qjs, and may pass in and out of the gastric cavity. 



My reasons for regarding the Discosoma anemone^ descriljed by M'Murrich, 

 as the Actinia heliantJms, of Ellis, are given at the end of the description of the 

 next species. 



Genus.— HOMOSTICHANTHUS, n. g. 



Discosomidfe, in which the tentacles are slightly knobbed and arranged in 

 numerous perijiheral cycles and radiating rows, a single row communicates 

 with each endocoele and exocoele. Column-wall devoid of verrucse ; disc much 

 folded. Two deep gonidial grooves. Sphincter muscle restricted.* 



The generic term has reference to the i^ractical similarity of all the rows of 

 tentacles, both endocoelic and exocoelic. 



*Prof. Haddon (1898, p. 432) employs this useful term for an endodermal sphincter muscle, in form 

 intermediate between the diffuse and the truly circumscribed types. It refers to an intermediate stage, 

 in which the mesogloeal plaitings, for the support of the musculature, do not arise from a common axis, but 

 from several principal axes of less complexity. He further suggests "constricted" for the typical cir- 

 cumscribed muscle, (cf. figs. 3 and 7, PI. xni., " diffuse endodermal muscle " ; fig. 6, PI. xii., " restricted 

 endodermal muscle"; figs. 1, PL xiv., fig. 2, PI. xv., "circumscribed (constricted) endodermal muscle "; 

 also, "aggregated," M'Murrich, 1893, p. 152, pi. xxii., fig. 23.) 



