Part II. — StichodactylinoB and Zoanthcce. 161 



tinuation of it. The retractor muscle extends over the whole face of the mesentery, 

 and similarly with the oblique muscle on the other face. 



llie mesenterial endoderm is a rather broad layer, and, in the upper region, its 

 cells contain numerous zooxanthellse. 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 Nesseldrtisenstreif 

 developed throughout their extent. This bears very large oval nematocysts 

 with the s^airal 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 stomodteal ectoderm, and are 

 nowhere very sharply marked o£E from the mesenterial epithelium (PI. xiii., 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 Smicti- 

 Thomce ; also at Laughlands, St. Ann, and at Port Antonio. Duchassaing and 

 Michelotti record it from St. Thomas, and ^PMurrich 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. 



Discosomidse, 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'. Fenti 



