THE ACTINIANS OE PORTO RICO. 
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within an axial entocoele, as in Forties and Cerianthus, no principal axial septum would be produced, 
but such is provided for in polyps built upon the Zoanthid type. 1 
Family ZOANTHIDS Dana. 
With definition of order. 
Subfamily BRACHYCNEMINZE Hadd. & Shackl. 
Zoantharia in which the sulcar element of the protocnemic sulco-lateral pair of mesenteries is 
imperfect. 
The above definition with regard to the sulcar element of the sulco-lateral pair being imperfect 
is not invariably true for all the individuals of a species. For in all the genera, except Sphenopus, 
included within the subfamily, polyps have been met with in which the mesentery referred to is 
perfect. In the paper on the Jamaican Zoanthece I have recorded that a specimen of Gemmaria variablis 
Duerdeu presented the normal brachycnemic arrangement on one side and the macrocnemic on the 
other. In a colony of Palythoci mammillosa Ellis & Solander, one polyp was brachycnemic on the 
right and macrocnemic on the left side; and in another polyp from the same colony the brachycnemic 
condition was on the left side and the macrocnemic on the right. Similar combinations of the micro- 
type were found in Palythoa caribsea Duchassaing & Michelotti, but one polyp was altogether macro- 
typic on both sides, in place of the normal brachytype. In the course of the present investigations a 
polyp of Zoanthus sociatus was found which was brachycnemic on the left side and macrocnemic on the 
right (fig. 16); and Carlgren (1896, pi. vm, fig. 6a) among other irregularities in a species of Isaurus 
found a polyp which was macrocnemic on the same side. Various other irregularities in the mesen- 
terial arrangement of different species of Zoanthids have been given by other workers; but apparently 
very rarely is there an actual replacement of one type by the other, as in the cases above mentioned. 
The numerous instances just cited are sufficient to indicate that the macrocnemic or brachy- 
cnemic type of mesenterial arrangement in the Zoanthidx is not so fixed as has been supposed, that in 
the same polyp both types may occur on different sides, or even the entire macrocnemic arrangement 
may appear in place of the brachycnemic. Still, by far the majority of polyps of any species exhibit 
the normal order established by Hertwig, Erdmann, and others for the particular genus, and the 
exceptions now and again met with should not be allowed to diminish the taxonomic value of the two 
subfamilies. Of six polyps of the Porto Rican Z. sociatus examined, only the one represented by the 
transverse section in fig. 16 showed any departure from the established order, and the many Jamaican 
polyps examined were all normal. 
Roule (1900) has recently suggested that the macrotypic genera Epizoanthus and Parazoanthus 
should disappear, and their representatives, along with those of Gemmaria, become united in the 
genus Palythoa. He goes so far as to place the Gemmaria swiftii of Duchassaing & Michelotti under 
the genus Palythoa , though I have shown (1898, p. 372) that its polyps, like, those of all the species 
of Parazoanthus, are macrocnemic and possess a diffuse endodermal sphincter muscle. 
Such associations as those proposed by Roule have reference mainly to the external appearance 
and habit of the colonies, and are wholly adverse to the principles of classification which hitherto 
have been found of the greatest value in Actinian studies. 
Genus ZOANTHUS Lamarck. 
Brachycnemic Zoanthidx, with a double mesogloeal sphincter muscle. The body-wall is in- 
crusted; the ectoderm is usually discontinuous; well-developed ectodermal canal system in the 
mesoglcea; monoecious or dioecious. Polyps connected by a thin lamellar ccenenchyme, stolons, or 
more rarely free. 
1 Since this was written I have been able to show (Johns Hopkins University Circulars, vol. xxi, No. 155, January, 1902) 
from an examination of numerous serial sections that the primary septa of the Rugose coral, Lophophyllum proliferum 
(MeChesney), are liexameral as in modern corals. Also that the later septa are added in such a manner as to leave no 
doubt that the mesenterial sequence bore the closest resemblance to that characteristic of living Zoanthids, except that 
in Lophophyllum new mesenteries and septa were added within four primary exocoelic chambers, whereas in Zoanthids new 
mesenteries arise in only two exocoelic chambers. Recent Zoanthids bear much the same relationship to the Palseozoic 
Rugose corals which living Actinians do to modern corals. 
