336 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The reflected ectoderm and mesenterial filaments are of the usual Zoanthean character, and for 
this species have been fully described by McMurrich in his paper “The Mesenterial Filaments in 
Zoanthus sociatus (Ellis),” 1899. The endoderm becomes greatly swollen below, where it contains an 
enormous quantity of pigment and nutritive granules of various kinds. Before receiving Professor 
McMurrich’s paper I had made numerous sections and drawings of the mesenterial filaments in this 
species, with a view to their study along somewhat similar lines to those followed in the above paper. 
My results as to the relationships of the intermediate tissues and ciliated bands, and also as to the 
very different character of the median part of the filament in its upper and lower regions, agree with 
those of McMurrich. I therefore merely give the figures and refer the reader to the latter’s more 
detailed account. My studies on this and other species lead me to regard the uppermost part of the 
median filament as a downgrowth of the stomodaeal ectoderm and the remaining part as endodermal, 
and, contrary to McMurrich, I am inclined to regard the intermediate streak as endoderm. 
No fertile polyps have been met with. 
Localities: Dominica (Ellis), Guadeloupe (Lesueur), Bahamas (McMurrich), Bermuda (Verrill), 
Jamaica (Duerden), Porto Rico (U. S. Fish Commission). 
Genus ISAURUS Gray. 
Large brachycnemic Zoanthidx, with a single mesoglreal sphincter muscle. The body-wall is 
unincrusted; the ectoderm discontinuous; ectodermal and endodermal bays and small canals in the 
mesogloea. Monoecious or dioecious. Polyps in small clusters or solitary. 
Carlgren (1896) has carried out investigations upon several examples of an undescribed species 
of Isaurus in order to determine the relationship of the external smooth and tuberculated areas, 
occurring in all the species of the genus, with the internal bilaterality exhibited by the mesenteries 
and stomodseum. One would naturally expect that the external symmetry would correspond with 
the internal. Carlgren finds that, as a rule, the smooth concave part of the column corresponds with 
the dorsal side of the polyp, or side on which the pair of microdirective mesenteries is inserted 
(sulcular), and the convex part of the column, bearing the tubercles, .corresponds with the ventral 
aspect of the polyp which bears the macrodirectives and the gonidial groove (sulcar). Although the 
tubercles may appear on both the right and left sides, it never happens that the smooth side is ventral; 
this belongs to the dorsal part of the body-wall. 
The relationships met with in I. duchassaingi scarcely conform with Carlgren’ s results. In the 
specimen from which fig. 23 was taken a very large tubercle occurs a little distance from the middle of 
the dorsal side, and in varying sizes they extend nearly all round. A section of this kind, however, 
is unsatisfactory for showing the actual relationships of the smooth and tuberculated area. Very thick 
sections of two other polyps of the Porto Rican Isaurus were therefore taken and are represented in 
figs. 24, 25. Fig. 24 gives the appearance in one of the polyps, the mesenteries appearing much broader 
than in thin sections. The lightly shaded area represents the surface of the section, while the dark 
area beyond indicates the projections on the lower part of the segment. Fig. 25 represents the same 
letails in the second polyp. In both, the narrow, smooth region of the polyp is wholly to the right 
side of the directive axis, but nearer the dorsal than the ventral border. The relationships were also 
checked on the entire polyp. It is clear from the figures that in none of the three polyps can the 
external bilaterality be said to correspond with the internal, as Carlgren found to be mostly the case 
with his specimens. 
Isaurus duchassaingi (Andres). Pis. II, VI, VII, Fig. 5, 23-26. 
Zoanthus tubcrculams, Duchassaing, 1850, p. 11; DueSassaing et Miclielotti, 1860, p. 327, pi. vm, fig. 5. 
Antinedia tuberculata , Duchassaing ct Miclielotti. 1866, p. 136, pi. vr, figs. 2,3. 
Antinedia duchassaingi , Andres, 1883, p. 544. 
Isaurus duchassaingi, McMurrich, 1896, p. 190, pi. xvn, figs. G-S; Duerden, 1898, p.346, pl.xvnu, fig. 4, pl.xvma, fig.5. 
Eight specimens of this peculiar Zoanthid were secured from Hucares, having evidently formed 
an isolated group in the same way that the sjiecies is found to occur around Jamaica and the Bahamas. 
In general the polyps, which are preserved in alcohol, are shorter and the transverse wrinklings ami 
tubercles more pronounced than in forms obtained around Jamaica and preserved in formol. Still the 
same essential external characters are displayed; the constancy with which the overhanging bilateral 
