A REVISION OF THK GENUS STEGANOPORELLA. 233 



tube appears to be traversed by three more or less transverse 

 lines. The most superficial of these, when seen from above, 

 is the line x, which indicates the bending round of the cryp- 

 tocyst to join the actual base of the tube. This appears, at a 

 deeper level, as the line y, where the recurrent part of the 

 cryptocyst bends round to form the upper wall of the tube. 

 This fold is indicated in optical section to the left of the 

 figure. The third line, z, in the plane of the basal wall of 

 the zooecium, is the origin of the deeper or basal part of the 

 wall of the tube. These relations are further explained by 

 the diagrammatic fig. 43, representing an ideal longitudinal 

 vertical section of the entire zooecium. 



The operculum of S. delicatissima is very much smaller 

 than the comparatively gigantic opercula of Stegano- 

 p ore 11a. That of the zooecium shown in fig. 42 measures 

 only 90 fx in diameter, while the smallest normal opercula of 

 any of the species of Steganoporella here considered 

 measure no less than 320 fx. There is at present no reason 

 for regarding the zooecia of Siphonoporella as dimorphic. 

 The opercula (in S. delicatissima) have a concentric 

 thickening bar, as in the "a opercula" of Steganoporella; 

 and the proximal ends of this bar project to a considerable 

 extent from the lower side in a direction at right angles to 

 the plane of the operculum. 



The question arises whether Siphonoporella should 

 be regarded as distinct from Steganoporella. I think 

 the answer to this must be in the afiirmative, while admitting 

 that the former shows many points of resemblance to certain 

 species of Steganoporella. Siphonoporella differs from 

 Steganoporella in the small size of its opercula (which in 

 S. delicatissima do not exceed 100 m in diameter), in 

 the absence of any horizontal proximal part of the crypto- 

 cyst, and in the fact that the "area" bounded by the 

 ''raised lines" and filled by the membranous epitheca is 

 usually not co-extensive with the front wall of the zooecium. 

 The cryptocyst of S. delicatissima is tubercular, but not 

 porous; the mouth of the tube may be surrounded above 



