J. E. Durerpen—Jamaican Actiniaria: Part T.—Zoanthee. 349 
elongated nematocysts, showing a spiral thread, occur sparingly. The mesogloea 
is thin, and small granular cell-enclosures are scattered throughout. 
The endoderm is a low band of cells resembling that of the mesenteries ; 
zooxanthellae, small nematocysts, and a weak muscle are present. 
Mesenteries.—The mesenteries are brachyenemic in type, and the perfect ones 
are arranged at about equal distances apart all round the cesophagus. Twenty-one 
pairs are present in one specimen. The endoderm is thin and crowded with 
zooxanthellz and small oval nematocysts. A parieto-basilar muscle and a verti- 
cally arranged musculature occur on each side. The mesogloea is well developed 
throughout.. Towards the insertion of the mesentery into the body-wall it is 
thrown into small irregular plaits or pennons ; still nearer it narrows a little. A 
basal canal and numerous irregular vertical canals and cell-enclosures occur the 
whole length of the mesenteries, continuous in places with those in the mesoglea of 
the column-wall. The reflected ectoderm rarely occurs, but the mesenterial 
filaments are met with as usual. ‘Towards the base of the polyp the mesenteries 
begin to unite with one another, and ultimately form a reticulum-like structure 
filling the whole of the ccelenteron. 
Gonads.—No gonads were present in three examples sectionized. 
From the latest researches of Professor M*‘Murrich, it appears that the West 
Indies possess two species of Isaurus, one from Bermuda, identified by him as the 
Isaurus tuberculatus, of Gray (1828), and another, the Zoanthus tuberculatus, of 
Duchassaing (1850), obtained from the Bahamas in the Northrop Collection, and 
previously collected from Guadaloupe and St. Thomas. In his Bermudan paper 
(1889 a), M*Murrich, however, considered Gray’s form as identical, not only with the 
Bermudan examples, but also with the Z. ¢uberculatus. Owing to these later results, 
and the specific name ¢uberculatus being occupied by both forms, he has followed 
Andres and adopted the term Duchassaingi tor the Bahaman examples and for those 
known to Duchassaing and Michelotti. 
Professor Haddon and Miss Shackleton (1891) have described as new, a form, 
I. asymmmetricus, obtained by the senior author from Torres Straits. In doing 
this they state (p. 684):—‘‘It is undoubtedly nearly allied to the JJammillifera 
tuberculatus of M*Murrich. ‘he specific differences are the lesser number and 
greater size of the tubercles, though their diameter is about the same, and their 
asymmetrical arrangement; the height of our species is about double that of the 
West Indian form.” 
The specimens described above seem to me to unite in a very marked manner 
the two West Indian and also the Torres Straits examples. I regard the differences 
in the external appearance of the tubercles, transverse annulations, &c., as largely 
dependent upon age and method of preservation. Even in the details of 
