434 E. M. Bri/doue—New Chalh Poh/zoa. 



Ooecia helmet-shaped and small, rarely present, and when present 

 fragile ; the specimen with oceeia from which Fig. 7 is taken is quite 

 exceptional. 



Avicidaria. None observed. 



The circular area restricted to the upper half of the zooeciura 

 distinguishes this species from any other of the lidded species yet 

 described. It occurs sparingly in the zone of A. quadratus, the 

 only zone from which I appear to have it. 



Membranipora pellicula, sp. nov. (PI. XXII, Figs. 9-12.) 



Zoarium always adherent, and so slightly raised as to be easily 

 mistaken by the naked eye for a skin of dirt or chalk. 



Zocecia sub-pyriform to pyriforni when not interfered with by other 

 zooecia, l)ut often in crowded spots losing all trace of pyriformity and 

 very variable in size; the area occupies normally about two-thirds of 

 the length of the zooecium and is a long narrow ellipse ; it is often 

 closed by a slightly convex lid in which there is a small elliptical pore 

 of variable position. 



Ooecia helmet-shaped, unusually long and distinctly squarish at the 

 upper end. 



Avicidaria very numerous and very small, being narrow pyriform 

 bodies with a smooth convex surface having a very narrow slit in its 

 upper half, which is rather abruptly elevated above its lower half. 



The extreme shallowness of the zoarium, the perforated lids, and 

 the small and abundant avicularia form a combination which readily 

 distinguishes this species from any other. It does not appear to occur 

 below the subzone of 0. pilula, in which it is very rare; but in the 

 subzone of A. quadratus and the lower part of the zone of ^. mucronata 

 it occurs freely. 



Membranipora Withersi, S[). nov. (PI. XXII, Pig. 13.) 



Zoarium always adherent. 



Zocecia faintly sub-pyriform, and having a slight internal front wall, 

 and tilted considerably, the head being much higher than the foot; 

 the area is a straightish-sided ellipse about '3 mm. long by "2 mm. 

 wide ; on the zocecial wall at the extreme head there is a pair of tiny 

 projecting tubes ; a little below them there is a pair of stout 

 perforated spine bases with an imperforate pair some way below 

 them ; beneath the oceeia the zocecial wall is very thin. 



Ooecia widely helmet-shaped, distinctly large in proportion. 



Avicularia of two kinds — one simple small pyriform bodies like those 

 of M. pellicida, but having a much wider aperture, and tilted like the 

 zooecia ; the other similar, but larger bodies lying horizontal and 

 having also a terminal aperture formed by the upper end being 

 sliced ofp by a downward and after a short way outward curving 

 ti'ansverse cut along a line which falls just within the upper end of 

 the horizontal aperttire, so that the two apertures are just continuous. 



At present I only know this species from the subzone of^. quadratus, 

 in wliich it is not uncommon. 



These four species illustrate well the gentle transition between 

 normal 2Iemb rani parte and the group which is generally assigned to 



