302 ESCHARHMG. 



thin and delicate in texture, and only slightly roughened. 

 The punctures show as mere circular depressions closed in 

 by membrane. Calcification, however, proceeds rapidly ; 

 and already in the second or third row from the margin of 

 the colony, ridges are growing up amongst the pores ; these 

 anastomose as they rise, and the original surface is very 

 soon concealed by a thick vitreous crust, pierced by as 

 many deep circular shafts as there were punctures on the 

 primitive wall. In the early state the peristome is ele- 

 vated ; but as the crust thickens, the orifice is on a level 

 with the surface of the cell. 



The zooecia are liable to some variation in form, and 

 are often much elongated and subquadrangular. 



The avicularium is generally small, with a rounded 

 mandible, and placed immediately under (and outside) the 

 lower margin ; but occasionally it assumes a lengthened 

 spatulate form. 



The var. fl, which Milne-Edwards has described as 

 Eschara bidentata (Plate L. fig. 4), is distinguished by 

 having a dentate process on each side of the orifice, and 

 overhanging it, which gives it a decidedly trifoliate ap- 

 pearance. In all other respects it seems to agree with the 

 normal form. These dentate processes are, I believe, 

 quite superficial. In certain states a thin membranous 

 envelope invests the cells, concealing the punctured crust, 

 and covering the zoarium with a smooth and somewhat 

 glossy epidermis. The lateral processes originate from 

 this superficial layer, and have no connexion with the 

 underlying calcareous crust. 



Occasionally the zoarium of L. foliacea assumes a 

 Hemescharine mode of growth ; but usually it is bilami- 

 nate, and its broad foliated expansions, variously contorted 

 and anastomosing freely, form large cavernous masses, 

 often of enormous size. Striking, however, as its habit is 



