112 PROCEEDINGS OF THE ACADEMY OF [1889. 



fuse type, which differs markedly in detail from that of D. delicatula, 

 the raesogloeal, processes being much more delicate and anastomosing 

 somewhat in their proximal portions (PI. VII, fig. 2). The circular 

 muscles of the column wall external to the dieitiform fronds 

 are fairly prominent, and are continued the entire way down the 

 column, not enlarging however to form a second sphincter. 



The tentacles are simple, conical, and of moderate length, and are 

 arranged in four cycles, their number being probably 96. By act- 

 ual count they seemed to vary somewhat, usually falling below that 

 number, but the discrepancies are probably due to the difficulty of 

 making a correct enumeration. They possess well-developed mes- 

 ogloeal processes for the support of the ectodermal muscles. The 

 disc is deeply folded in, internal to the tentacles, so as to form a deep 

 fosse around the peristome (PI. VII, fig. 1), which, however, does not 

 rise above the level of the margin. I was not able to distinguish in 

 any of my preparations the delicate raesogloeal processes of the disc 

 which support the ectodermal muscle cells in D. delicatula, but it is 

 possible that they had been macerated away. 



The mesogloea of the stomatodreum is raised upon its ectodermal 

 surface into prominent but rather delicate ridges, over which the 

 ectoderm is folded. The gonidial grooves are deep, and as in Ou- 

 lactis are prolonged below the level of the internal opening of the 

 stomatodoeum, and have the mesogloea thickened. In D. delicatula 

 Hertwig describes the gonidial grooves as being hardly marked in 

 the stomatodseum, and if this is found to be an invariable character- 

 istic, it will be necessary to alter slightly the definition of the Phyl- 

 lactidre given above. The depth of the grooves, and their prolonga- 

 tion downwards, is so marked in the other members of the group 

 that I have examined, as to suggest that its apparent shallowness in 

 the specimen examined by Hertwig may be due to distortion. 



The primary and secondary mesenteries are perfect throughout 

 the whole length of the stomatodseum ; the tertiaries are perfect in 

 their upper part, but lower down separate from the stomatodreum ; 

 while the fourth cycle consists entirely of imperfect mesenteries. 

 The directives are attached throughout a greater part of their 

 length than are any of the other mesenteries, owing to the pro- 

 longation of the gonidial grooves. The longitudinal muscles in the 

 upper portion of the mesenteries form a low band, covering the 

 greater portion of the non-gonophoric region of the mesentery; in- 

 ternally the muscle processes end rather abruptly, but externally they 



