SC1IIZOPORELLA SINUOSA. 267 



Zocecia subrhomboidal or irregularly ovate, flattened in 

 front, slightly elevated towards the orifice, bounded by 

 a prominent sinuous line; surface granular, large fora- 

 mina round the base of the cell, and frequently scattered 

 over the entire surface ; orifice, in its earliest stage, 

 arched above, lower margin straight, with a rounded 

 sinus in the centre, peristome thin, unarmed ; at a 

 more advanced stage suborbicular, produced below, 

 peristome raised. Ocecia rounded, depressed, subim- 

 mersed, granular, frequently with a single large pore 

 on the front. 



Colonies forming subcircular, flat, glossy crusts, of a rich 

 red colour. 



Var. a (armatd). With a small avicularium within the 

 mouth on the lower margin; mandible rounded (Plate 

 XLII. fig. 2). 



RANGE OF VARIATION. This species exhibits some very 

 remarkable variations, dependent chiefly on the extent to 

 which calcification has proceeded. The mouth com- 

 pletely changes its character at different stages of growth, 

 the primitive shape being more or less concealed by a 

 secondary formation, which surrounds and partially over- 

 hangs the original aperture. As it appears in young colo- 

 nies or in marginal cells, the mouth is almost semicircu- 

 lar, with a straight lower margin, which is hollowed in the 

 centre into a rather broad rounded sinus. The secondary 

 aperture, which is found in the older portions of the 

 colony, and which closes in the original opening, is sub- 

 orbicular, more or less produced and pointed below. The 

 latter character varies considerably ; and, especially towards 

 the edge of the crust, the lower secondary margin is often 

 without the sinus. 



The surface is usually granular, covered with minute 

 wart-like prominences. The large foramina are sometimes 

 confined to the border of the cell, but very frequently they 

 are scattered over the surface. Thev are filled in by a 



