SCHIZOPORELLA DISCOIDEA. 265 



SCHIZOPORELLA DISCOIDEA, Busk. 

 Plate XXX. figs. 8, 9. 



Lkfiulia DISCOIDEA, Busk, Quart. Journ. Micr. Sc, Zoopbjtol. vii. (1859), 

 66, pi. xxii. figs. 7, 8 ; ibid. viii. 144, pi. xxvii. figs. 4, 5 ; 

 ibid. viii. 283: Hincks, Quart. Journ. Micr. Sc, Zoophytol. 

 viii. 276, pi. XXX. figs. 4, 4 a. 



Alysidota conferta, Busk, Eep. Brit. A.ssoe. 



Zocecia ovate^ punctured or granular, surrounded by a 

 raised line, disposed in linear series, which radiate 

 regularly from a central depression ; orifice slightly 

 raised, arched above, lower margin straight, with a notch 

 in the centre ; peristome, in fertile cells, much elevated 

 in front ; oral spines 6-7 ; on one side (or on both 

 sides), a little below the mouth, a small raised, oval 

 avicularium, mandible directed dowuAvards ; frequently 

 replaced in the marginal cells by a long linear avicularium 

 slanting outwards. Ooecia globose, recumbent, punc- 

 tured, hooded. 



Colonies small, forming subcircular patches, slightly de- 

 pressed in the centre. 



Range of Variation. The surface of the cells, which is 

 smooth and punctured in an early condition, becomes more 

 calcified with age, and the punctures are surrounded by 

 roughened ridges of stony matter ,• in a more advanced 

 stage the walls are much thickened and granular. The 

 chief variations occur in the number, shape, and distribu- 

 tion of the avicularia. The elongated form is almost 

 confined to the young or marginal cells, and is by no 

 meaus always present upon them. It usually occurs in 

 pairs, one on each side of the mouth. Occasionally, but 

 very rarely, it is met with on one of the inner cells. In 

 most cases it is replaced by a small raised avicularium, 

 situated a little below the mouth, sometimes on both sides, 



