386 ESCHARID^. 



granular, glossy, punctured round the edge ; orifice 

 (adult) suborbicular, somewhat elongated transversely, 

 Mdthin the lower margin a curved hook-like process, and 

 immediately below it a tall sharply pointed mucro ; peri- 

 stome elevated, rising on one side, or on both sides, into 

 a strong spinous process, on the upper margin (in young 

 cells) two long and slender spines ; frequently below 

 the orifice a mound-like swelling bearing at the upper 

 end a large aviculanum, placed transversely with a 

 strong beak and a pointed mandible ; on the lower part 

 of the cell a raised, projecting avicularium with an 

 acute mandible. Ooecia more or less immersed, semi- 

 circular, smooth or granular, generally with a prominent 

 mucro on the front, the opening closed by a smooth 

 calcareous operculum, white or yellowish white. 

 Colonies forming large crusts, of a delicate lilac colour 

 when fresh. 



Range of Variation. The specific diagnosis is founded 

 on fully developed cells ; but in different stages of growth 

 the species presents a very different appearance, and, in 

 a large proportion of cases, some of the structures which 

 I have described are wanting. Colonies frequently occur 

 in which the large transverse avicularia are either absent 

 altogether or very sparingly developed ; in well-developed 

 patches I have frequently been unable to find one of them. 

 "When they are present they conceal the curved process 

 on the lower margin, which is so characteristic of the 

 species. In the absence of the mound and avicularium, 

 the mucro rises from the lower lip of the secondary orifice. 

 The spinous processes on the side of the mouth vary in 

 number and are sometimes wanting; and the two true 

 spines on the upper margin are rarely to be found, except 

 on the edge of the colony. I know of few species^ if any, 

 which appear in such varied guise as the present. 



In the interior of the colonv the cells are crowded. 



