324 ESCHARID^. 



Colonies forming large, circular, reddish patches, very 

 compact and neat in appearance. 



Var. a [Belli, Dawson). Zooecia flattish, granular, sepa- 

 rated by a deep sinuous and punctured furrow ; the front 

 wall carried up on each side of the orifice into a digiti- 

 form process (Plate XLVI. fig. 6). 



Var. /S {fjracilis). Zooecia elongate, punctured over the 

 entire surface (Plate XLVI. fig. 9). 



Range of Variation. This species changes its appearance 

 considerably with age and the attendant thickening of 

 the calcareous crust. It also assumes many varietal 

 forms ; but the difierences which it exhibits are mainly 

 superficial, and, with the exception of the avicularium, 

 no important element of structure is much affected. 

 When old it becomes coarsely granulous, and of a dead- 

 white colour, the mouth is surrounded by a thick collar- 

 like extension of the crust, the walls are massive, the 

 perforations often very distinct and numerous, and the 

 avicularium is sometimes obliterated, probably by the 

 calcareous overgrowth. 



The form of the mouth is very constant ; and that of 

 the cell itself is subject to but slight variation. But the 

 differences in superficial character are numerous and 

 striking. The surface is more or less granular ; the 

 marginal punctures are sometimes a marked character, 

 but often they are altogether wanting * ; frequently the 

 mouth is surrounded by an elevated collar ; in some cases 

 this is replaced by a prominent umbo, immediately below 

 the avicularium, and in others the whole central portion 

 of the cell is mamillated. In other cases, again, tlie 



* The marginal punctures may, I think, be regarded as an essential 

 character, though they are often obliterated by the thickening of the cell- 

 walls. 



