A REVISION OF THK GENUS STEGANOPORELLA. 289 



with less everted border than in the specimen jBgured. The 

 opening of the tube is usually just visible from above, although 

 it is nearly vertical. The basal wall of a is largely exposed 

 from above, since the cryptocyst is inserted at a great dis- 

 tance from its distal end. In b, although the lateral recesses 

 are very deep, their floor (formed by the cryptocyst) usually 

 slopes so as to meet the base of the distal wall, or the distal 

 end of the basal wall. Although the tube may be complete 

 distally, it is commonly incomplete. In a it appears to be 

 asymmetrical, one wall joining the lateral wall of the zooccium, 

 the other joining the basal wall (fig. 12). It is also often 

 asymmetrical in b (as in fig. 12), and this is correlated with 

 a curious difference in the lateral recesses. While the floor 

 of the left one (in the figure) joins the lateral and distal 

 walls only, that of the right one, while joining these two 

 walls, dips down medianly at its distal end to meet the basal 

 wall on the distal side of the tube. In other words, the 

 cavity of the right lateral recess (in this particular zooecium). 

 reaches the basal wall at a small region in or near the middle 

 line of the distal end of the zooecium ; and this results in the 

 formation of a small circular or slit-like mark (fig. 32) on the 

 back of some of the zooecia. This is, of course, not present if 

 the cryptocyst joins the distal wall only. It may, however, 

 be regarded as a common character of this species. It may 

 be noted that the vertical walls of this species are very thick 

 and strong. 



I have not found distinct epithecal sclerites. The b 

 opercula (fig. 41) have nearly always six to eight strong 

 curved distal teeth (counting the two corner ones, which are 

 often specially large); and there are usually two to four on 

 each side besides ; this number is not often exceeded. In 

 one case minute interstitial teeth were observed, as in fig. 44 

 (S. magnilabris). The opercula have the usual delicate 

 border outside the strong submarginal sclerite ; and it is 

 obvious that this flange is of importance in fitting closely 

 over the zooecium, and being so thin as to leave no edge 

 which could be lifted up by any intruding animal. The 



