207 



3rd Subdivision: Pseudostega. 



The boundaries of the separate zowcia are not shown on the surface of the 

 colony, which on the other hand is divided into a number of deepened areas, 

 the number but not the extent of wliicii corresponds with (he separate zoa>cia. 

 No pores or spines, hidependent aviciilaria without calcified transverse bar be- 

 tween the opercular and the subopercular area. The ocrcia, situated in the distal 

 part of each zotrcium, are inner spaces in the frontal wall of the zooecia and 

 open outwards through a variously shaped opening. 



Family Membranicellariidae n. f. 



The zoa'cia have an oval aperture surrounded by a raised rim with onlv the 

 distal part filled by a membranous opercular valve. 



Membranicellaria (n. g.) dubia Busk. 



? Melicerita dubia Busk, Challenger, Zoology, Vol. X, Part I, 1884, 



pag. 97, PI. XXXIII, fig. 1(). 



(PI. VII, figs. 2 a— 2 e). 



The surface of the colony is divided by distinct suture-like separating lines 

 into broad depressed areas of a rhombic or hexagonally rhombic form (the two 

 neighbouring areas sometimes only meeting in a lateral corner, sometimes in a 

 shorter or longer edge) and in the greater part of their circumference they have 

 a more or less distinctly bounded, rather narrow, thickened, prominent marginal 

 part, which however most often disappears be^'ond the centre of the two proxi- 

 mal separating lines. Each area has a large, oval aperture in the centre, the dis- 

 tal margin of which is very slightly curved, and with the exception of this it is 

 encircled by a pretty broad, projecting marginal portion. The entire surface of 

 the cryptocyst is closely set with small round tubercles, which are most plentiful 

 in the boundary ridges of the areas and in the marginal portion surrounding the 

 aperture, and are arranged in more or less regular transverse rows. In the middle 

 of the basal part of the distal wall a large, single-pored rosette-plate is seen, half 

 surrounded by an arch-shaped collection of small, single-pored plates, and the 

 distal half of each lateral wall has a similar group. The membrane covering the 

 colony presents a system of linear, chitinous thickenings corresponding with the 

 furrows between the separate areas, and a similar curved chitinous thickening 

 separates the covering-membrane from the free margin of the opercular valve. 

 The largei' opercular valve has a membranous frontal surface, but a well chiti- 

 nized and strongly developed opercular arch and lastly, it may be mentioned 



