110 THE BERMUDA ISLANDS. 



PHYLLACTIDJE. 



Some points of considerable importance as regards the char- 

 acteristic structure of the members of this family have been ob- 

 tained from the study of the two forms which I include here 

 within it. The family was established by Andres* for forms in 

 which the disc is furnished towards the center with simple 

 tentacles and towards the periphery with foliaceous fronds. In 

 one of the forms about to be described the fronds are replaced 

 by short digitiform tentacles arranged in a single cycle, but 

 nevertheless it agrees in other structural points with Oulactis, 

 and I have therefore found it necessary to alter the definition 

 of the family, placing importance on internal anatomical 

 structures rather than upon external characteristics. 



In the first place, in the Oalactis about to be described, and 

 in Diplactis, as I propose to name the genus to which the form 

 with tentacles replacing the fronds will be referred, a sphinc- 

 ter 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 tentacles and the peripheral 

 fronds or tentacles. In 0. flosculifera from the Bahamas this 

 sphincter was not observed, but was probably overlooked in 

 the single specimen I obtained for study, and none of the prep- 

 arations 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 dis- 

 tance below the inner margin of the stomatodseum ; the histo- 

 logical structure also of the ectoderm lining the grooves differs 

 slightly from that of the general surface of the stomatodeeum, 

 it is not thrown into folds as it is elsewhere, and the mesogloea 

 of the grooves is thickened. 



I would define the family PhyllactidaB as follows : Actininoe 

 in which the disc is furnished with simple tentacles towards 

 the center and with a cycle of short digitiform tentacles or 



*A. Andres. Le Attinie. fauna und Flora des Golfes von Neapel, Aluno- 

 graphie ix. 1883. 



