J. G. WALLER ON CLIONA CELATA, ETC. 261 



the excavations of another " borer," of which this pebble gives an 

 example. As here, so in huge boulders of all sizes, which lay- 

 strewn around, there was what, in the geologist's term, we may call 

 " denudation." The outer crust, which covers the burrow in the 

 perfect state, was broken away in large patches, and thus made 

 conspicuous, what might otherwise have easily eluded vigilance, from 

 the very small size of the orifices. But when I had informed myself 

 of this character, I at once instituted a rigid search and examination, 

 breaking away perfect portions to find, what I really expected to do, 

 the " borer Sponge." But not a single instance, on this or another 

 occasion, ever greeted my eye, and I do not believe it is ever seen in 

 these excavations at all.* 



A close examination, however, will convince us, that the work must 

 be made by a similar, if not the same creature, and this is the more 

 inevitable when we proceed to a microscopic examination. I again 

 call your attention to my diagrams. First, to the drawings of these 

 contiguous cups, which do not seem to be continuous, or generally 

 at least to anastomose the one with the other ; but to be separate 

 dwellings, each with its own aperture. (PI. XX, Fig. 2.) A still closer 

 examination shows us that the creature, wishing to enlarge its 

 burrow, or to seek its food, whichever it may be, proceeds to make a 

 new excavation at the base centre, sometimes at the sides, but not 

 often, apparently, interfering with his neighbour (Figs. 11, 12.) And 

 this invariably begins by a new orifice of the same small diameter as 

 that, which is external, and by which it entered. But in the example 

 before you, I never find any deeper workings than about a quarter of 

 an inch. All these are perfectly clean, and without any extraneous 

 matter, except in the instance referred to, which was completely 

 superficial, and in an uncovered burrow caused by the " denuda- 

 tion." 



Let us now bring the microscope to bear upon these workings, 

 and, at a glance, we find the same sub-circular depressions as in 

 the burrows of shells. (Fig 8.) There is the same character, 

 the same interference or section of the circular boundary, 

 and the diameter is the same, viz., the 500th of an inch.f In fact, 

 the precision of the cuttings all declare them to be by a similar, 



* I thonght I had found a minute dried piece of it. Bat on mounting it 

 I discovered it was a mixture of extraneous matter, particles of sand and a 

 few acerate and pin -shaped spicules, which appeared to me to belong to 

 Hymeniacidon suberea. 



t Owing to a slight error in the drawing, they appear larger. 



JouEN. Q. M. C, No. 47. x 



