176 



of the anler. Their calcified ectooau-ium is generally devoid of pores, and their 

 aperture is closed by a horizontal ciij)-sha])ed chitini/ed operciiluni which is 

 connected at its base with the opercuhiin of the gonozooecium. 



The zooecia are usually rectangular, and the aperture has a somewhat raised 

 anter and generally a more or less broadly rounded sinus between the two more 

 or less distinct hinge-tcclh. Immediately on the distal side of these is a more or 

 less distinct line, (most clearly visible on PI. VI b, figs. 2 a, 8 a i.<: 6 a) which 

 curves outwards and is continued into the line forming the boundary between 

 the narrow marginal edge and the cryplocyst. In 77i. expansd (PI. VI b figs, f) a 

 — 5 e) and VVi. mdinilluris (PI. Via, figs. 5 a — 5 e) the aperture has contrary to 

 the rule a proximal margin which is straight or almost straight, and in VVi. Rozieri, 

 var. Idhidld (PI. VI, figs. 6 a — Oj) the sinus is filled more or less completely by 

 a lip-shaped process, (figs. 6 f , (> g). The line mentioned above, which curves 

 outwards on the distal side of the binge-tooth, forms the boundary between the 

 cryptocyst and the gymnocyst, the latter occupying the region on the distal side 

 of this line. While the aperture in some cases e. g. in 77i. luuHte liollandiae (PI. 

 VI a, figs. 3 a — 3 f) takes up the whole or almost the whole of the breadth of 

 the zoa'cium distally, so that the gymnocyst is exclusively or mostly represented 

 by the anter of the aperture, it is in most cases j)re.sent on either side af the 

 aperture as an area developed to a varying extent and in diflerent ways, which 

 we may term the adoral area-. This is sometimes developed in the form of a 

 level or slightly arched surface, obliquely ascending towards the distal margin, 

 or sometimes the whole or part of its surface is taken up by an acropetalous 

 spine, most often short and wide with a broadly rounded terminal part, (PI. 

 Via, figs. 4 a, 5 a) seldom more like an ordinary spine (PI. VI b, figs, lb, 1 c, 

 2 a). The calcification of these spines takes place in a number of narrow longi- 

 tudinal belts, and accordingly their surface is radially striated more or less sharply, 

 and the growing spine also ends in a crenulated margin. The development of 

 the adoral area is however subject to great variation within the species, and it 

 may even l)e different on the two sides of the same zooecium. 



The cryptocyst, which forms the whole of the remaining calcified part of the 

 frontal wall of the zooecium within the raised margins of the lateral walls has 

 as in the species of Ste(janoporeUd a more or less developed crenulated marginal 

 part, and apart from the outgrowths from the two opesiuhe it has its greatest 

 depth at the proximal end of the polypide-tube, that is to .say, in a line carried 

 through the |)roximal margin of the two opesiula;. This Wuv, which lies some- 

 what proximally to the centre of the zocrcium, forms the approximate distal 

 limit for the appearance of pores. The two opesiuhe, which enclose between 



