STUDIES ON THE COMPARATIVE ANATOMY OP SPONGES. 515 



I. The Genus Ridleia, n. gen. 



This genus, which I wish to dedicate to my friend and late 

 colleague, the Rev. S. O. Ridley, who is so well known for 

 his work on Sponges, may be diagnosed as follows : 



" Sponge corticate, with a highly-developed system of fibrous 

 tissue. Consisting of a single solid body terminating above in 

 an osculum which leads into a well-defined oscular tube with 

 fibrous walls. Spicules monactinal, styli or tylostyli, confined 

 almost entirely to the ectosome. Skeleton composed chiefly of 

 stout longitudinal bands of spicules situate in the inner portion 

 of the ectosome, and of tufts of small spicules projecting at 

 the surface of the Sponge. Canal system canalicular, flagel- 

 lated chambers diplodal." 



A generic diagnosis based upon a single species, especially 

 when only a single specimen is present, must be more or less 

 tentative, and very possibly future investigations upon fresh 

 material will lead to a modification of the above. 



Ridleia oviformis, n. sp. 



External Characters. — The single specimen in the collec- 

 tion (fig. 1) consists of an egg-shaped body terminating above 

 in a slight papilla upon which lies the small osculum, and 

 thinning out below into a flattened peduncle. The peduncle 

 appears, from the existence of certain flattened surfaces (a a), 

 to have been attached to pebbles during life, in a manner 

 similar to that which occurs in Quasillina (fig. 8). 



The specimen is 15 mm. in height and 7 mm. in greatest 

 breadth. It has a very compact, cork-like consistence, and its 

 colour in spirit is pale yellow. 



The osculum (figs. 1 and 2, o) is single, very minute, and 

 situate on a small papilla at the summit of the Sponge. 



Arrangement of the Skeleton. — The skeleton is almost 

 entirely confined to the ectosome, or that outer portion of the 

 Sponge in which there are no flagellated chambers. Its most 

 important constituent is a ring of stout, longitudinally dis- 



