400 CELLEPORID^. 



C. pumicosa varies indefinitely in general appearance. 

 Sometimes it forms small oval masses on tlie stems of 

 zoophytes. When developed on the surface of shells &c., 

 it takes the shape of a somewhat circular mound, raised 

 in the centre, and sloping off towards the edge. Some- 

 times the surface of the zoarium is distinctly nodulous. 

 Frequently it occurs in irregularly shaped porous masses 

 of very considerable size, composed of many layers of 

 crust placed one upon another, and involving more or less 

 the fragment of shell or other body which constituted the 

 original site of the colony. A specimen of this kind from 

 Torbay measures 3| inches in length by 2^ in width. 



The cells in the older portions of the colony are per- 

 fectly erect, the apertures looking straight upwards ; they 

 are separated by spaces, which are occupied at a lower 

 level by the orifices of other cells. The younger marginal 

 zooecia are decumbent, bright and silvery, and of delicate 

 texture. The large and orbicular mouth, without any 

 trace of sinus, and the strongly developed mucro in the 

 centre of the lower margin (which encroaches slightly on 

 the aperture), bearing a pointed avicularium at the bottom 

 of its inner surface, are the most marked distinctive fea- 

 tures. The total absence of the spatulate avicularia, which 

 are so abundant on most of the other British species, is 

 also a good (negative) character. The mucro varies con- 

 siderably in size and proportions, but is commonly tall, 

 and rises above the avicularium into a slender and sharply 

 pointed spike. The avicularium itself is generally turned 

 a little sideways. 



The surface of theocEcium seems to be generally entire ; 

 but in some specimens it is punctured ; the punctures are 

 large, circular, reniform, or wedge-shaped. 



A variety occurs in which the ovicells are not only punc- 

 tured, but bear, in most cases, a rather large avicularium 

 on each side, with a pointed mandible. 



