1867.] DR. J. E. GKAY ON SPONGES. 531 



Gaimard, one being a large conical siliceous sponge, and the other a 

 small branched calcareous one. And why are these sponges called 

 Alcyonoid? They have no affinity to Alcyonium, which are true 

 zoophytes. 



3. Heterotella. 



The tube short, rather irregulai*, conical, truncated, irregularly 

 netted. Skeleton formed of thick bundles of very numerous slender 

 spicules, placed in all directions, and forming an irregular network, 

 similar to the network of the lid of Euplectella. 



Heterotella corbicula. (PI. XXVIII. fig. 2.) 



Alcyoncellum corbicula, Valenc. Mus. Paris ; Bowerb. B. Sp. i. 

 p. 176. 



Hub. Isle De Bourbon. 



I am indebted to Prof. "Wyville Thompson for having first drawn 

 my attention to the want of the regular longitudinal fascicule of spi- 

 cules in these two genera, and also for most kindly presenting me 

 with the photographs of the two sponges taken from the specimens 

 in the Paris Museum, which are here copied. 



Fam. 2. EsPERiADiE. 



Skeleton composed of fusiform and Unear spicules, interspersed 

 with anchorate, bihamate, or birotulate spicules, which are either 

 attached to the membranes or scattered in the sarcode, and form a 

 defence to the sponge. 



The bihamate and anchoi-ate spicula exist in large numbers on the 

 surface of the interstitial membrane. The bihamate are fusiform 

 spicula, bent at each end into the form of a hook, the curves being 

 in the same plane or at right angles to each other, the tips are 

 tapering and acute, or sometimes solid and club-shaped ; and rarely 

 they are expanded into circular plates. 



The anchorate spicula always have their two terminations in the 

 same position as those of the bow of an ordinary ship anchor. In 

 some sponges they are tolerably uniform in shape and proportion ; 

 while in others they vary exceedingly, not only while in course of 

 development, but even when in their adult condition. They glide 

 so insensibly from one form into another that it is difficult to draw 

 a distinction between them, even when there are a sufficient number 

 of fully developed ones to exhibit the normal form. 



In most cases, besides the large and fully developed anchorate 

 spicules, there is found accompanying them a secondary series, which 

 are very much smaller in size, and vary exceedingly both in sym- 

 metry and amount of development ; they appear to be simply abor- 

 tive developments of the larger and more perfect of the normal spi- 

 cula. Tlie anchorate spicula are gradually and progressively deve- 

 veloped. They are to be found at both sides of the membranaceous 

 skeleton, and are often very minute (see Bowerb. Phil. Trans. 1858, 

 pp. 205, 300, 303). 



