A REVISION OF THE GENUS STEGANOPORELLA. 249 



cryptocysfc is not much depressed proximally, and is thick, 

 with rather large pores. Some asymmetry in the floors of 

 the two lateral recesses is not uncommonly noticed; and the 

 asymmetiy, when present, is indicated on the basal wall. 

 This is usually very characteristic, and is distinguished by 

 the occurrence of a large distal region, limited proximally by 

 the insertion of the cryptocyst, and often covered by a wall 

 which is much thinner than the rest of the basal wall, so that 

 the tube is clearly visible through the fenestra thus formed. 

 In the single b zooecium examined the descending part of 

 the cryptocyst meets the basal wall and the two lateral walls 

 at a long distance from the distal wall. The epithecal 

 sclerites are rather long and conspicuous, and start from the 

 base of the operculum. The epitheca is thin and trans- 

 parent. 



The single b operculum examined of the t^^pe-specimen 

 (fig. 14) has eight well-developed teeth, most of which are 

 conspicuously long, and apparently weak and flexible. They 

 are confined to the distal part of the submarginal sclerite, 

 which fades away proximally. The main sclerite is D-shaped, 

 and the operculum has a distinct basal sclerite. The a oper- 

 cula (fig. 15) have two very conspicuous distal teeth on the 

 main sclerite. The sclerite/, which acts as a buttress to the 

 proximal projection of the main sclerite, appears in this 

 species at least to be a hollow prolongation of the main 

 sclerite which runs into the chitin of the outer surface of the 

 operculum. 



The opercula of this species are as variable as the calcare- 

 ous parts. While those of the specimens (&) agree with the 

 type-specimen except in having somewhat shorter teeth in 

 the A form, those of specimens from other localities are 

 somewhat different. The b opercula are always rare, and I 

 have been able to examine only one of specimen {d) and one 

 of (/). In the former (fig. 16), from the Mergui Archipelago, 

 there are nine stiff erect teeth, the distal ones being long; 

 the edge of the main sclerite is at a considerable distance 

 from the border of the operculum. The teeth of a are 



