106 PROCEEDINGS OF THE ACADEMY OF [1889. 



replacing the fronds will be referred, a sphincter of the diffuse type is 

 present, but instead of being situated upon the column wall below 

 the margin, it occurs internal to the margin, between the inner ten- 

 tacles and the peripheral fronds or tentacles. In 0. floa- 

 culifera from the Bahamas this sphincter was not observed, but was 

 probably overlooked in the single specimen I obtained for study, 

 and none of the preparations which I still possess include the region 

 in which the sphincter should occur. Secondly in the two species 

 of Oulactis which I have studied, and in the Diplactis, the gonidial 

 grooves are very deep and are prolonged a considerable distance be- 

 low the inner margin of the stomatodseum ; the histological structure 

 also of the ectoderm lining the grooves diners slightly from that of 

 the general surface of the stomatodseum, it is not thrown into folds 

 as it is elsewhere, and the mesogloea of the grooves is thickened. 



I would define the family Phyllactidse as follows : — Actinina? in 

 which the disc is furnished with simple tentacles towards the center 

 and with a cycle of short digitiform tentacles or more or less folia- 

 ceous fronds towards the periphery; a sphincter of the diffuse type 

 occurs upon the inner surface of the disc between the inner tentacles 

 and the outer tentacles or fronds ; and the stomatodseum is provided 

 with two deep gonidial grooves which are prolonged some distance 

 below the inner extremity of the stomatodseum. 



The family Phyllactidse was placed by Andres in the suborder 

 (family) Stichodactylinse, the fronds being considered homologous 

 with tentacles. I have here ventured to remove the family to the 

 suborder Actininse, and it will be necessary to furnish my reasons 

 for such a change. The tentacles must necessarily be considered 

 outgrowths of the disc, since structurally they resemble it closely 

 while differing greatly from the column. Are the fronds also disc 

 structures? 



The question turns upon what we shall consider to be the limit 

 between the disc and the column. The majority of authors have 

 taken a more or less distinct fold of the body wall, the margin, fre- 

 quently furnished with conspicuous acrorhagi, to be the boundary, 

 and certainly in many cases there seems to be a marked difference on 

 either side of this fold. Thus the column may, as in Bunodes and 

 Phymactis, be tuberculated as far as the margin, but beyond this the 

 tubercles cease, and there is apparently a decided difference between 

 the region below and that above the limiting fold. 



