A REVISION OB' THE GENUS STEGANOPOKELLA. 273 



The characters of this species are sufficiently well marked^ 

 though it is distinguished by a considerable amount of varia- 

 bility. It is encrusting or Escharau, possibly sometimes 

 Hemescharan. The slight descent of the cryptocyst is shared 

 only by S. haddoni, and to a less extent by S. truncata. 

 The combination of a b operculum thickened in a A-like 

 manner with an '^ undifferentiated" a operculum is only found 

 in S. haddoni of the species at present known; and this 

 differs from S. buskii in the great relative size of the b 

 zooecia, and their enormous oral shelf, besides many details 

 in the b opercula, and in particular the restriction of the 

 teeth to the distal half. 



The edge is thin and rather distinctly separated from the 

 post-oral shelf, which is narrow, small proximally, and is 

 covered by sharp tuberculations which ma}' give it a denti- 

 culate appearance. The oral shelf is not much more de- 

 veloped in B than in A. The condyles are conspicuous in b, 

 smaller in A. The oral arch is well raised ; a transversely 

 elongated fenestra (or semi-transparent part of the distal cal- 

 careous wall) within the oral arch in a and b is conspicuous 

 in some specimens (a), and indicates the extent to which the 

 zocecium overlaps the next in the series. The cryptocyst is 

 sharply separated from the post-oral shelf ; it is thin, with 

 conspicuously large pores, and slopes gently, without any 

 angulation, into the cavity of the median process and the 

 floor of the lateral recesses. Some specimens show the 

 cryptocyst in a very simple condition. Its descent in (c) is 

 unusually slight, and there is nothing to distinguish the 

 commencement of the floor of the lateral recesses except the 

 cessation of the pores of the horizontal part. The median 

 process, although of the typical form, is small and has an un- 

 usually shallow cavity, whose floor is nearly in the same plane 

 as that of the lateral recesses. The margins of the median 

 process are not continued to form a proximal boundary to 

 the lateral recesses. The opening of the tube is entirely 

 visible from above ; it is nearly circular, completed as usual 

 by the distal wall, its lateral walls being so low as to appear 



