Pi'of. W. Thomson on the " Vitreous " Sponges. 129 



the normal form. I am not quite satisfied on this point even 

 now. As I am precluded from using either of Dr. Gray's 

 names, I substitute one Avhich I had in MS. before I saw Dr. 

 Gray's paper. 



H. corhicula^ Valenciennes (sp.). PL IV. fig. 1. 



Alcyoncelhim co7-hicula, Val. (in Paris Museum) ; Bowerbank, British 



Spongiadee, vol. i. p. 176. 

 Heterotella corbicula, Gray, Proc. Zool. Soc. 18G7, p. 531. 



The Sponge is tubular, shaped somewhat like a wine-glass, 

 about 4 inches high and 2 inches wide across the lip, and tapers 

 downwards somewhat irregularly to a diameter of 1| inch at 

 the base. The wall of the cylinder is formed of a rather thick 

 irregular network of delicate siliceous spicules, from *01 to '5 

 inch in length, loosely arranged in fascicles which cross one 

 another at low angles, and are loosely connected and com- 

 bined by a small quantity of very soft mucilaginous sarcode, 

 which, in the dried sponge, remains as a thin yellowish film. 

 These cords curve upwards and downwards and round, anasto- 

 mosing in all directions, and leaving between them rounded 

 openings of various sizes, and show no tendency whatever to 

 a regular longitudinal and transverse direction. All the long 

 spicules are formed on the hexradiate type ; but the four 

 secondary rays are usually abortive, being represented merely 

 by four tubercles at right angles to one another, about the 

 middle of the main shaft, which is somewhat enlarged and 

 tuberculated at each end (PI. IV. fig. 1 c). The spicules 

 have, according to the ordinary plan of sponge-structm-e, a 

 delicate centre canal, which sends off four short radii to the 

 four secondary tubercles. The walls of the spicules consist of 

 concentric layers of silica separated by films of sarcode, which 

 can be readily shown discoloured by burning in a spirit-lamp. 

 This structm-e can be best studied in the long spicules of Ih/a- 

 lo7iema, which are in every respect, except in size, essentially 

 the same. 



Scattered among the long spicules of the skeleton, there are 

 many fully developed hexradiate spicules. Some of these are 

 perfectly regular in form, the rays smooth and nearly equal 

 (PL IV. fig. 1 b) ; but many of them are irregular, the rays 

 are distorted and bent (fig. 1 a), and in some cases two or 

 more are irregularly united together. I have little doubt tliat 

 these latter indicate the first stage, as it were, to the formation 

 of a continuous network such as we find in EupJectella and 

 Ajphrocallistes. In Habrodictyon^ however, the coalescence 

 never occurs to any extent, and the network remains perfectly 

 flexible and without a trace of the raised filigree ridges which 



