228 SIDNEY F. HARMER. 



proximal wall. It may also occur on the distal wall, giving 

 valuable specific characters, and when present here it is found 

 as a projection within the oral arch, and at a considerably 

 deeper level (fig. 13). 



Immediately on the basal side of the shelf a porous "cal- 

 careous lamina" takes its origin from the proximal and 

 lateral walls, forming a layer more or less parallel to the 

 epitheca. This is the "cryptocyst" of Jullien,^ and the 

 space between it and the epitheca is the " hypostegia" of the 

 same author. The Microporid^e, Steganoporellid^, with the 

 Membraniporidae and certain other foi-ms, are grouped to- 

 gether by Jullien as Diplodermata," in allusion to the occur- 

 rence of a cryptocyst distinct from the ectocyst. In most of 

 these forms the cryptocyst is not complete, but has a free 

 internal edge which limits an opening of varying size, the 

 " opesia." 



The cryptocyst of Steganoporella is always complete 

 proximally. As it passes distally, it sinks towards the basal 

 wall — in some species with a slight angular deviation from 

 the epitheca, in which case it joins the distal wall of the 

 zocecium (figs. 11 and 13) at a greater or smaller distance 

 from its base. In other species the cryptocyst descends 

 steeply, often at right angles to its proximal portion, to join 

 the basal wall (fig. 10). The importance of the place of in- 

 sertion of the distal border of the cryptocyst as a specific 

 character has hitherto been completely (werlooked. Since 

 the calcareous walls are more or less transparent, it follows 

 that in some species the basal wall seen from below shows 

 inerely the origin of the four vertical walls, while in others 

 it shows in addition the insertion of the edge of the crypto- 

 cyst (fig. 27). This structure is developed as an outgrowth 

 from the proximal side of the zooecium, which in its young 

 state passes through a condition, with incomplete crypto- 

 cyst and large opesia, which is permanent in species of 

 Membranipora. 



' 'Bull. Soc. Zoo). Fiimce,' vi, 1881, p. 4 (sep.). 

 2 See also Jullien, ' Cap. Horn ' (t. cit.), p. I. 66. 



