1889.] NATURAL SCIENCES OF PHILADELPHIA. 105 



the base, the longitudinal grooves there becoming radiating and 

 the transverse ones concentric. 



The only character which is markedly different from what occurs 

 in the West Indian specimens of the species is presented by the 

 longitudinal muscles of the mesenteries. The middle portion of a 

 section through the muscle-band presents an appearance quite similar 

 to that to be seen in the West Indian form, and the internal edge is 

 also the same, the long mesogloeal processes terminating abruptly, 

 and being followed by smaller processes which extend to the com- 

 mencement of the reproductive region of the mesentery; but to- 

 ward the insertion of the mesenteries into the column wall the ar- 

 rangement is slightly different (PI. VI, fig. 3). In the Bahama speci- 

 mens the mesogloea between the outer edge of the muscle-band and 

 the insertion of the mesentery into the column wall is thin, and the 

 muscle-band gradually thins out externally. In the Bermuda forms, 

 however, the longitudinal muscle begins abruptly, and the mesogloea 

 external to it is thick with short, stout muscle processes ; or, as in the 

 directives, with the muscle cells, instead of appearing to cover proc- 

 esses, presenting rather the appearance of here and there dipping 

 down slightly into the mesogloea. 



CI? * o 



It is not probable however that this slight difference is to be re- 

 garded as specific, and since in other respects there is almost exact 

 correspondence, the Bermuda forms must be considered identical- 

 with those from the Bahamas. 



Family PHYLLACTIDiE. 



Some points of considerable importance as regards the character- 

 istic structure of the members of this family have been obtained from 

 the study of the two forms which I include here within it. The 

 family was established by Andres 1 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 ar- 

 ranged in a single cycle, but nevertheless it agrees in other struct- 

 ural 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 Oulactis about to be described, and in Di- 

 plactis, as I propose to name the genus to which the form with tentacles 



1 A. Andrei. Le Amnio. Fauna un I -Flora des Golfes von Neapel Mono- 

 giaplne ix. 1883. 



