HEXACTINI^ FROM NEW SOHTH WALES. 51 



therefore more easily removed than in Pliellia broioni, and the underlying 

 structures are less destroyed in the process. Both mucus and a cuticle 

 cover the surface of the ectoderm of the column and lower capitulum, and 

 the ectoderm underlying these structures is narrow and badly preserved. 

 In the naked distal portion of the capituluin the ectoderm is much wider 

 (PI. 6. fig. 15, dxap.), consisting of very deep coluuniar cells, and nemato- 

 cysts, which are not numerous, appear to be confined to this portion. 



Small ill-defined bodies, probably badly preserved isolated cells, are 

 scattered irregularly through the mesogloea and occur in the sphincter also, 

 where they are easily detected, being of much larger size and staining deeper 

 with carmine than the muscle-cells of the sphincter itself. An endo.dermal 

 muscle lining the coelenteron is present on unbranched mesogloeal plaitings, 

 which do not appear to be further developed in the capitular region (PI. 6. 

 fig. 15, end.m.). The endoderm forms deep triangular ridges between the 

 mesenteries (PI. 6. fig. 17, end.). 



Sphincter. — The sphincter, large and mesoglceal, lies throughout its course 

 nearer the endoderua than the ectoderm (PI. 6. fig. 15, spli.). Less powerful 

 than in Pliellia hrowni, it has the same double form as in that species, lying 

 chiefly in the lower capitulum, with a second marked expansion in the naked 

 distal portion where it occupies the full width of the mesoglffia. The muscle- 

 cavities are very numerous, small, oval or round, lined with muscle-cells and 

 embedded in an irregular manner in the mesogloea. These cavities lie singly 

 and retain their own shape, but there are very few scattered cells, and the 

 shape of the sphincter as a whole is compact. The naked portion of the 

 capitulum and the distal expansion of the sphincter which it contains are 

 more or less constant in shape in this specimen, thus forming a great contrast 

 to the long prolongations of both capitula of the sphincter which are 

 present in the last species, Pliellia hroumi. This difference is probably not 

 specific, but the result of Phellia capitata being in full expansion, while 

 Pliellia broioni is in a contracted state. See Verrill (4) on the sphincter of 

 Pliellia panamensis, later named Phelliopsis panamensis (22). The ectodermal 

 side of the sphincter is irregularly waved, and it reaches its greatest width 

 at about the centre of its leno'th. 



Tentacles (PL 6. figs. 15, 16). — The tentacles are thick-walled with a 

 small lumen. The ectoderm, the broadest of the three layers, is well supplied 

 with uematocysts and has a broad nervous zone. The ectodermal muscle is 

 powerfully developed on branched processes of the mesogloea, which end in 

 the nervous zone of the ectoderm, as in the last species, and are therefore 

 not mesogloeal in position. Short and almost unbranched on the outer side 

 of the tentacle, these mesogloeal processes are at least twice as broad on the 

 inner side which faces the oral aperture (PI. 6. figs. 15, 19, ect.ni}, ect.m.^). 

 The mesogloea, which is narrow, bears on its internal border a well-marked 

 ectodermal muscle. The endoderm is deeply folded. 



