Dr. Bowcrbank on llyalonema mlrabilis. 397 



cartilage-pit ; they are triangular instead of leaf-like, and slightly 

 incline inwards instead of being erect. 



M. truncata of Searles Wood, from the Coralline Crag, is a 

 comparatively large, squarish, and flattened shell, and has long 

 cardinal teeth. 



L. — On Hyalonema mirabilis, in reply to Dr. Gray. 

 By Dr. Bowerbank. 



[n the 'Annals and Magazine' for October 1866, p. 287, Dr. 

 Gray has published a note " On the 'Glass-rope' Hyalonema,'' in 

 which he has criticised the short observations on that genus in 

 the first volume of my Monograph of the British Spongiadce. 

 Those observations were never meant to be taken as a history of 

 the anatomy and physiology of that curious animal, but simply as 

 an introduction to the genus Hyalonema among the Sponges, and 

 as a reason for figuring the numerous interesting forms of its sili- 

 ceous spicula among those of various other species of Sponges. 

 The detailed account of these organs, except as far as it was neces- 

 sary to illustrate the specimens selected for figuring, was reserved 

 for a paper shortly to be published, and especially devoted to a 

 minute investigation of the whole of the organization of the 

 animal, including the basal mass of sponge-tissue, the spiculous 

 axis, or rope, and its coriaceous envelope, with a view to establish 

 the organic unity of these parts as portions of one and the same 

 animal. 



The criticisms of Dr. Gray are therefore somewhat premature; 

 and in some respects he has so far misrepresented my opinions 

 as to render a reply to his observations necessary. But in thus 

 answering his remarks it must be understood that I shall not at 

 present attempt to decide the questions in dispute, as to whether 

 it be a single animal or two animals, the one parasitical on 

 the other, and that I shall reserve the structural proofs and the 

 reasonings necessary to such a decision for a paper on the sub- 

 ject, which I have long had in preparation and which I hope 

 shortly to be able to publish. 



In page 289 Dr. Gray writes, "Again, the specimens being 

 sunk in a sponge that had a flat base by which it was attached 

 to some marine body, I concluded that the natural habit of the 

 animal was to develope itself in a sponge, so as to support itself 

 in an erect position ; and this idea was strengthened by finding 

 that the sponge near the part where the coral perforated it was 

 of a more condensed and harder texture than tlie other parts of 

 it. I concluded that there was a kind of mutual understanding 

 (such as we often find between animals that are parasitic on one 



