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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
(1890) of C. americanus shows certain divergences, which make me hesitate in regarding it as this 
species. Without a thorough comparison of the two side by side it would be hazardous to establish 
the Porto Rican representative as a new species. I have since been endeavoring to secure specimens 
of the Carolina species for comparison, but so far without success. I therefore defer the description 
of the present specimen until its distinctness or otherwise can be established. Both McMurrich and 
H. V. Wilson have obtained at Nassau, Bahama Islands, larvae of a Cerianthus, which may perhaps 
have been derived from polyps of the same species as the Porto Rican examples. 1 have never met 
with a Cerianthus around Jamaica. 
ZOANTHARIA (restr.). 
Zoantkex , R.Hertwig,1882: Haddon, 1891; etc. 
Zoanthiniaria, van Beneden, 1897. 
Zoantharia (restr.), Carlgren, 1900. 
Actinozoa in which six primary mesenteries (protocnemes) arise bilaterally. The ventral or 
sulcar directives become complete, the dorsal or suleular directives and the sulcar moiety of the 
protocnemic dorso-lateral pairs remain incomplete, while the sulcar moiety of the ventro-lateral pair 
is incomplete in one group (Brachycneminte) and complete in another (Macrocneminse). Additional 
mesenteries (metacnemes) arise independently (i. e. neither in pairs nor symmetrically on each side) 
within the exocoele on each side of the sulcar directives, and become arranged in unilateral pairs, 
constituted of an incomplete and a complete moiety. 
Only the perfect mesenteries are fertile and bear mesenterial filaments with both glandular streaks 
and ciliated bands. A single sulcar gonidial groove is present. The ectoderm of the column- wall 
is devoid of a muscle and ganglion layer, and the mesogloea is traversed by irregularly branching 
ectodermal canals or by scattered groups of cells. The body-wall is usually incrusted with foreign 
particles. The polyps are generally grouped in colonies connected by a coenenchyme, the coelenteron 
of each polyp communicating with that of the other members of the colony by means of basal 
endodermal canals. 
I have already given the reasons for which the tribe Zoantheee has been erected into an Anthozoan 
division equivalent to the Ceriantharia, Aetiniaria, Alcyonaria, etc. It includes only one family, 
which therefore carries with it the definition of the order. It is of interest to note that though 
filaments do not occur on the imperfect mesenteries of adult Zoanthids yet McMurrich (1899) has 
found the glandular streak to be present on the V and VI developmental ] >ai rs in egg embryos, as 
well as indications of the filament in the micro-directives, all of which never reach the stomodseum. 
The mesenterial arrangement characteristic of the Zoantharia (restr.) suggests in many ways the 
mesenterial sequence which must have been followed by the polyps which produced certain types of 
Palaeozoic corals. The formation of the calcareous septa in corals is found to conform very closely 
with that of the mesenteries, both as to order of appearance and adult arrangement, just as do the 
tentacles. In the Palaeozoic family Zaphrentidie the septa are disposed pinnately with regard to two 
primary axial septa, the “main” and “counter” septa of palaeontologists, and two other primary septa, 
the lateral or “alar” septa, can also be distinguished. If the mesenterial plan of the Zoanthid repre- 
sented in lig. 2, plate A, be compared with the septal plan of a Zaphrentoid coral, such as Streptelmma, it 
will be seen how very closely the mesenterial spaces of the former correspond with the septal scheme 
in the latter. From the known relationships of the soft parts of a coral to the hard parts there is the 
greatest suggestiveness in the primary mesenterial plan of a Zoanthid to “main,” “counter,” and 
“alar” septa, while a pinnate addition of the later mesenteries is characteristic of the ventral aspect, 
which would correspond with the pinnate septa in the counter quadrant of the Zaphrentoid. 
The septal plan of Streptelasrna as given by Ivunth, and in the palaeontological text-books of 
Zittel and Nicholson, indicates that the mesenteries were added in the primary exoccelic chamber on 
each side of one of the pairs of directives, just as in the Zoanthidx; but in the fossil coral another 
similar series of mesenteries appeared in the next primary exocoele on each side. In modern Zoan- 
thids only two exoccelic regions of active growth persist beyond the protocnemic stage, but in the 
extinct Zaphrentoids there were four. The main, counter, and alar septa are the. septa formed within 
the primary entocoelic chambers. Where mesenterial increase is simply bilateral at one region 
