A UEVlSrON OF THE GENUS STEGANOPORELLA. 229 



The cryptocyst extends througli the body-cavity of the 

 zooecium, which thus occurs both above it and below it. Its 

 descending pai't is never developed so much as to form a 

 complete septum across the body-cavity, but it is always 

 perforated by a more or less circular hole (fig. 13). Through 

 this passes the tentacle-sheath of the polypide, which oc- 

 cupies the chamber on the basal side of the cryptocyst. The 

 tentacle-sheath does not completely fill the hole, so that 

 there is a free communication between the two parts of the 

 body-cavity. 



The opening in the distal part of the cryptocyst is the 

 base-line of a calcareous " tube," which projects into the 

 distal or subopercular chamber of the zooccium. That part 

 of the tube which is remote from the ba.^al wall is always 

 well developed, and is usually clearly visible from above. 

 The structure which is thus seen as a projection from the 

 descending part of the cryptocyst is what I shall hereafter 

 term the "median process/' whether it is merely the upper 

 wall of the tube (fig. 7) or is complicated by the outgrowth 

 of flanges, as in fig. 11, etc. 



In species in which the cryptocyst descends vertically to 

 the basal wall, the opening of the tube is vertical, and cannot 

 be seen (fig. 2) unless the zooecium is looked into obliquely 

 from the distal end. In those in which the cryptocyst joins 

 the distal wall the opening is oblique, and can usually be 

 readily seen from above (fig. 13). The sides of the tube are 

 generally much less developed than its roof, and there may 

 be no tubular wall on the basal or distal side. In this part 

 the opening may be completely surrounded by the crypto- 

 cyst, of which it is a mere perforation, surrounded laterally 

 and above by upstanding walls (fig. 11, large zocecium). In 

 other cases (fig. 11, small zocecium) the cryptocyst is still 

 more incomplete, the sides of the tube usually diverging and 

 joining the basal or distal wall, according to the arrangement 

 of the cryptocyst. The position of the opening and the 

 extent of its tubular walls offer valuable specific characters. 



The tube, which thus rises from the free surface of the 



