SCHIZOPORELLA AURICULATA. 261 



equal width throughout, very slightly, if at all, expanded 



at the extremity. 

 Colony a large, irregular crust, of a dull-yellow colour 



when dead. 

 Var. /9 (cuspidata). With a conspicuous spike-like process 



on the front of the ovicell ; avicularium very prominent. 



(Plate XXIX. n ? . 8.) 



RANGE OP VARIATION. S. auriculata is liable to many 

 variations, some of which involve a remarkable change in 

 the appearance of the species. Many of these variations 

 are due to the different degrees of calcification which 

 mark the different stages of growth, and which are also 

 probably to some extent dependent on diversities in 

 habitat. In their youngest state the cells have the walls 

 thin and perfectly smooth, and more or less punctured. 

 They are soon, however, enveloped in a crust composed of 

 anastomosing ridges, amongst which the punctures are 

 visible. This is their normal adult condition. But in 

 some cases the thickening of this secondary envelope is 

 carried to an extraordinary extent. The cells are buried 

 so deeply beneath a mass of coarse reticulated crust, that 

 the mouth and avicularium, instead of being on the surface, 

 are placed at the bottom of a kind of circular shaft. The 

 character of the ovicell is also much affected by the 

 development of the calcareous covering. It is sometimes 

 so much enveloped by it, that it appears as a very slight 

 swelling on the surface of the zoarium. At other times it 

 is partially inclosed by the crust, a somewhat semicircular 

 space being left free in front. In some cases the zoarium 

 is overspread by a white granular crust. Besides these 

 differences, which are due to calcification in its various 

 degrees, there are others in the form and position of the 

 avicularium which have a special interest. In its normal 

 condition this appendage is small and almost circular, 



