BIMERIA RIC4IDA SP. X. O 



caulus is quite small, but there is uo inwardly projecting shelf 

 or diaphragm. 



Near the base of the calyx the perisai-c is of moderate, 

 uniform thickness. Slightly higher it is raised into ridges, 

 and these ridges become more pronounced towards the 

 edge of the cup, and vaiy in number according to the 

 number of the tentacles. The perisarc of the ridges is 

 apparently of firmer consistency than that between, since it 

 stains much more intensely. The tentacles are surrounded by 

 tubes of perisarc, and these have a greatly thickened lower 

 wall or floor which is directly continuous with the ridge 

 running down the calyx. This lower wall resembles the 

 ridge in staining deeply. The upper wall of the perisarc- 

 tube surrounding the tentacle is exceedingly thin, and is 

 sometimes almost evanescent ; it is continuous with the thick, 

 soft, perisarc covei'ing the hypostome region of the polyp (fig. 

 9, s. pr. t.). 



The perisarc of the hypostome region is of very consider- 

 able thickness, and it completely envelopes it (fig. 3, s. pr.). 

 Thin perisarc stains only faintly, and it has an especially 

 roughened outer surface to which inorganic particles, diatoms, 

 etc., become attached. It is of a soft, gelatinous natui-e, and 

 does not appear to inhibit the power of contraction and 

 expansion of the body to the extent that would be expected. 

 It is continuous with the thin layer of perisarc forming the 

 upper wall of the tentacle-tubes. 



With regard to the soft parts of the polyp, there is a 

 peculiarity about the mouth, which appears to be unique 

 among the hydroids. When the polyp is in a state of rest 

 there is a small rounded aperture at the apex of the hypo- 

 stome (fig. 4, 0. e. c), and the soft perisarc extends to the edge 

 of the opening. The aperture leads into a small, lenticular, 

 ectodermal chamber with a convex floor (figs. 3 and 5, e. c). 



The mouth proper is a small aperture in the centre of the 

 floor of the chamber. The mouth when slightly open appears to 

 be four-cornered. The shape arises through the occurrence in 

 the upper portion of the coelenteron of four wide and greatly 



/Q^-.^ -«».«»-^ >N^ 



j uj ( L I B R A R Y 



