366 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The diameter of the base is about 5 cm., and the height of the column 4 cm. The diameter of 
the disk usually varies from 10 to 12 cm., or may be more in fully expanded specimens. The tentacles 
are about 0.6 cm. in length, and are often largest in diameter toward the tip, where they may measure 
0.2 cm. across. The diameter of the naked part of the disk is about 2.5 cm. 
Anatomy and Histology . — The basal disk is of considerable thickness. The ectoderm is an excep- 
tionally broad layer and contains many narrow, elongated gland cells with granular contents; the 
mesoglcea presents delicate plaitings on its endodermal border for the support 'of a well-developed 
circular endodermal musculature. 
The column-wall is of only moderate thickness; the ectoderm is deeply folded, the mesoglcea 
partly following. Numerous long granular cells are included among the supporting cells, and the 
mesoglcea presents a delicate fibrous structure with many connective-tissue cells. On the endodermal 
surface the latter forms narrow branching plaits for the support of the circular musculature. The 
endoderm is much thinner than the other t.wo layers and contains many zooxanthelke and granular 
gland cells. At the verrucse the ectoderm consists almost wholly of supporting cells, gland cells are 
absent, and the ciliation is more obvious. Histologically, therefore, the organs most closely resemble 
the sucker-like verrucae of other Actinians. 
The sphincter muscle is strongand circumscribed, and made up of several lobes, sothatitsoutline 
varies in different transverse sections. The pedicle is broad and short, and a narrow mesogloeal axis 
extends nearly the whole length. 
Both the entocudie and exoccelic tentacles are simple outgrowths of the disk, with the three 
constituent layers of about equal thickness. Long, narrow nematocysts occur in a peripheral zone 
toward the apex. The endoderm is crowded with zooxanthelke and coarsely granular gland cells. The 
endodermal and ectodermal musculatures are developed, the latter being the stronger and associated 
with a nerve layer. 
The discal ectoderm is nearly devoid of nematocysts and contains granular gland cells. The 
mesoglcea is deeply plaited on its endodermal border for the support of the circular muscle, while the 
radial ectodermal muscle is weak. 
In young polyps the mesenteries are arranged in hexameral orders, but the regularity is lost in 
older specimens. One young example possessed twelve pairs of perfect mesenteries, an alternating 
cycle of twelve pairs stretched about halfway across the disk, and another cycle of twenty-four pairs 
extended just beyond the column-wall. In another polyp thirty-six pairs of mesenteries reached the 
stomodaeum. Older polyps seem to possess merely an alternation of complete and incomplete pairs. 
At the insertion in the column-wall the mesenteries are narrow and then thicken abruptly, 
the retractor muscle extending nearly across the face, again terminating in an abrupt manner in the 
imperfect pairs, but gradually in the perfect members. The face of the mesentery where the retractor 
muscle is well developed is somewhat undulating. The endoderm is loaded with coarsely granular 
cells. The parieto-basilar muscle is weakly developed. The inner mesenterial stomata are large, 
while the parietal are small circular apertures. The basilar muscle is well developed, of the type rep- 
resented for Asleractis e.vpansa and Bunodosorna spherulata. Gonads may occur on all the mesenteries. 
Localities: West Indies (Ellis) , Guadeloupe, St. Thomas, etc. (Duchassaing & Michelotti) , Bahamas 
(McMurrich), Jamaica (Duerden), Porto Rico (U. S. Fish Commission). 
Another large West Indian Discosomid, Ilomostichanthns anemone (Ellis) Duerden, is rarer than 
the former, and is not represented in the Fish Hawk collections. Both species appear to be absent 
from the Bermudas, not being recorded by McMurrich or Verrill, but A. helianthus is plentiful at the 
Bahamas. 
Carlgren (1900«, p. 76) has pome to the opinion, first adopted by McMurrich, that Ellis’s figures 
of Actinia, helianthus and A. anemone are best regarded as representing only one species. In Turin, „ 
Carlgren had the opportunity of examining one of Duchassaing A Michelotti’s specimens, which 
these authors had named 1). anemone , and states that it is the same form as that described by 
McMurrich under this name. He then observes that Ellis’s original figure of A. helianthus are without 
doubt referable to the same form as that which Duchassaing & Michelotti and McMurrich had under 
consideration, and therefore accepts my determination of it as D. helianthus. It becomes necessary, 
therefore, that the Jamaican form I identify as D. anemone should be given a new name. In the 
“Nachschrift” (p. 117) Carlgren suggests ITomostichanthus duerdeni. 
