31G SIDNEY F. HAllMER. 



the operculum and the median pore can be explained in the 

 same way as Jullicn's "coruicula" mentioned above. 



Levinsen (1891, p. 285) states that the median pore, like 

 the other pores, is closed by a membrane. 



Microporella ciliata,^ Pall. 



'J'he compensation-sac is like that of M. malusii, wliicli 

 this species further resembles in the grouped condition of the 

 parietal muscles. I have not made out the details of the 

 opening of the sac. There is a membranous portion in the 

 tongue of the crescentic pore, as in M. malusii. 



(e) Microporoid Genera. 



Micropora, sp.~ (figs, 57, 58). 



The large lateral foramina serve for the transmission of 

 the tendons of the depressor muscles (fig. 58, depr.) of the 

 frontal membrane, as correctly stated by Jullien (1888, 4, 

 pp. 77 — 81, pi. xiv, fig. 1), who terms them " opesiules." 

 The opesiule is a complete calcareous tube (/.?*.), the base of 

 which joins the basal wall or the lateral wall of the zooecium, 

 the two conditions often occurring on opposite sides of the 

 same zooociuui. The tube usually gives off a curved lamella 

 (fig. 57) on its distal side, near tiie basal surface. From the 

 recess thus formed originates the occlusor muscle {occL), 

 whose long tendon passes obliquely to be inserted into one of 

 the lateral corners of the vertical flange of the operculum. 

 The depressor muscle [dcpr.) is much stronger. Its iibres 

 converge to a tendon which passes through the opesiule 

 and is inserted into the frontal membrane. I regard these 

 muscles as a special development of the parietal muscles, 

 which are otherwise unrepresented. The calcareous frontal 

 wall {crypt.) is complete, and the relations of the depressor 

 muscles indicate that it is a cryptocyst. 



' llincks (1880), p. 200. 



- Tones Slruits, A. C. liuddou Coll. 



