256 SIDNEY l'\ HARJIEU. 



strong, aud ankylose with tlie distal margin of the median 

 process^ thereby forming an unusually massive support for 

 the base of the operculum. The oral arch is well raised. 

 The cryptocyst is sharply separated from the post-oral shelf, 

 and is slightly tubercular. The pores are small, and do not 

 usually occur on the part of the cryptocyst which descends 

 into the median process, being here obliterated by a tuber- 

 cular calcareous thickening. The tube is complete, though 

 the only part of its wall which is well developed is the upper 

 part. The lateral parts of the wall are very low, while 

 basally the tube is a mere perforation in the oblique crypto- 

 cyst. The epithecal sclerites are minute and widely separated 

 from the operculum. They are probably small, because the 

 epitheca generally is so thick that it is strong enough to 

 withstand the pull of the depressor muscles without differen- 

 tiating special sclerites. In the dry condition a somewhat 

 complicated appearance of sclerites seems to be present in 

 the epitheca. As these cannot be seen in Canada balsam 

 preparations, I have convinced myself that they are due to 

 the crumpling of the epitheca during drying. 



I have found only one form of operculum (fig. 18) ; the 

 similarity of these to the b opercula of S. sulcata (and 

 particularly to that of specimen /) induces me to regard them 

 as belonging to the b type, in which case we have here the 

 unique peculiarity of a species in which the b opercula alone 

 are known. In the absence of any certain evidence as to the 

 meaning of the dimorphism of Steganoporella, it is not 

 impossible that some species consist of two kinds of colonies, 

 in one of which the a form of zooecium preponderates or is 

 alone present, and in the other the b form. If this were the 

 case it would not be inconceivable that S. connexa might 

 be the second form of S. simplex or S. auriculata, for 

 instance. The supposed species are not unlike in some 

 respects ; but I do not think that they are really related in 

 this way. 



The cliitin of the opercula, and in particular that of the 

 sclerites, is thick and dark- coloured. The occlusor tubercle 



