Part Il.—Stichodactylinee and Zoanthee. 161 
tinuation of it. The retractor muscle extends over the whole face of the mesentery, 
and sunilarly with the oblique muscle on the other face. 
The mesenterial endoderm is a rather broad layer, and, in the upper region, its 
cells contain numerous zooxanthelle. Clear mucus is sometimes seen in the 
act of being extruded from many of the cells, and an occasional granular gland 
cell is present. 
The mesenterial filaments have only the central portion or Nesseldriisenstreif 
developed throughout their extent. This bears very large oval nematocysts 
with the spiral thread somewhat loosely arranged. They are located in the 
deeper parts of the filaments, and a narrower kind occurs at the margin. The 
filaments can be traced in connexion with the stomodeeal ectoderm, and are 
nowhere very sharply marked off from the mesenterial epithelium (PI. xu, fig. 1). 
No reproductive organs were present in the half dozen examples sectionized. 
The species is found very abundantly, in water of three or four feet, growing 
on the coral rock around all the Port Royal Cays associated with Actinotrix Saneti- 
Thome; also at Laughlands, St. Ann, and at Port Antonio. Duchassaing and 
Michelotti record it from St. Thomas, and M*Murrich from the Bahamas. 
The polyps are always aggregated in patches, often several feet across, as a 
result of their usual method of reproduction by fission. ‘They display but little 
activity in opening and closing, the extended condition being by far the more 
usual. An excessive amount of clear mucus is given out on handling, rendering 
it very difficult to remove them from their attachment, and interfering somewhat 
with their proper preservation. 
Genus.—STOICHACTIS, Haddon. 
Discosoma, . . . M°Murrich, 1889, 1893; Kwietniewski (pars), 1898. 
Stoichactis, . . . Haddon, 1898. 
Discosomidze, usually of large size; column smooth below, and with verrucee 
above. ‘Tentacles vary in form, from moderately short and subulate, to short and 
blunt, and even to quite small and capitate ; not more than one row communicates 
with a mesenterial chamber. Sphincter muscle strong and circumscribed. 
Generally two gonidial grooves. 
Consequent upon the researches of Dr. J. A. Simon (1892), on the type species 
of Discosoma—D. nummiforme, it was clear that some of the species included under 
the genus would have to be separated. For forms similar to the West Indian 
Discosomid, which M°Murrich first anatomically investigated, Haddon erects the 
above genus and includes, in addition, two Australian representatives—S. Ment 
