104 B. W. PRIEST ON THE CALCAREA. 



Grantia ciliata belongs to this Family, and is certainly one of the 

 prettiest as well as interesting forms of the Calcarea found on our 

 coast. It is parasitical on Algae, Zoophytes, &c, and likewise 

 dredged from eight to ten fathoms. It varies in size, the largest 

 that has been found being about three inches in length. The 

 sponge elongately oval, sometimes globular, slightly pedicelled ; 

 surface papillated, hispid. Cloaca central, cylindrical, nearly as 

 long as the sponge ; armed internally with spiculated, equi- 

 angular, tri-radiate spicules; spicular ray attenuated. Mouth of 

 the cloaca armed with a thick ciliary fringe of very long and 

 slender acerate spicules ; base of the fringe supported by large, 

 short and stout fusiform acerate spicules. Oscula simple, very 

 slightly depressed from the surface of the cloaca. Pores incon- 

 spicuous. Interstitial cells, distal terminations more or less 

 obtusely conical, furnished with a ciliary fringe of slender acerate 

 spicules. Skeleton spicules equi-angular tri-radiate. Besides the 

 spicular defences of the mouth of the cloaca, there is often a 

 membrane found at the base of the neck of the cloacal orifice, 

 forming a sort of diaphragm. It appears probable that besides 

 being able to close the mouth of the cloaca by the approximation 

 of the distal termination of the ciliary spicules, it lias also the 

 power of completely closing it by the extension of a veiling 

 membrane or diaphragm. In the same way the pores of the 

 sponge are protected and hidden by similar ciliary spicules, the 

 mechanism of which is simple and interesting. In the process of 

 inhalation of water and distension of the distal extremity of the 

 interstitial cell, the cone of spicules is expanded into a cylinder, 

 causing the access of nutritive particles to the pores. When the 

 action ceases a collapse of the cell ensues, and the distal points of 

 the spicules again approach each other, thus stopping anything 

 from entering the pores. 



We now come to the Leucones, which are modifications of the 

 Sycones, their flagellated chambers being complete homologues of 

 the radial tubes; their exhalent canals owing their origin to the 

 invaginations of the inner cavity, and their inhalent canals re- 

 garded as homologous with the inter-canals of the Sycones, so 

 that these families approach nearer to the same type than in the 

 majority of sponges. 



Leuconia nivea, being an example of this Family, may often be 

 met with, appearing as white crusts on the under surface of rocks 



