J. G. WALLER ON CLIONA CELATA, ETC. 257 



bound. It belongs to the cover not the book. Now, not only does 

 this simulate those of the excavators in shells externally, but also 

 the burrows, to a great extent. (PI. XX, Figs. 1, 3, 4, 6.) There 

 is, indeed, nothing wanting to show both cause and effect. Being 

 perfectly familiar with the operations of this creature, as well as 

 itself, both as beetle and larva derived from the volume in question, 

 my conclusions are formed by its study. 



This leads me, then, now to consider the aspect of the com- 

 mencement of the work on the shell. It is, of course, from the 

 outside, as one might suppose, and begins by a small circular speck 

 which enlarges as it proceeds, sharp and well defined, sometimes 

 throwing up a furrow like ridge, before a complete perforation is 

 made, but cutting always with the utmost precision. There are also 

 to be found signs of the nature of the tool's operation moving in 

 the segment of a circle, but it is not easy to describe them.* 



Having now considered the external orifices, let us enter the 

 cavities and examine the mechanical action therein declared. And 

 we must bear in mind the characteristics of the substance, whether 

 of limestone or of shell, because the operation will not be exactly the 

 same in each. Nevertheless, there will be general principles found 

 in both, which are unmistakable and point to the same operator. 



That which at once strikes us is, that the excavation is made by 

 a series of consecutive circular cuttings, intersecting each other 

 irregularly by segments, with sharp ridges between them, and sharp 

 points at the boundaries. The whole surface is thus tesselated with 

 so many depressions, assuming geometric forms, all produced by 

 tangental sections of circles. It is remarkable for the precision of 

 the work. No softening, no blurring, no indefinite outline ; but 

 one that is distinct, hard, and well marked. Continue our search, 

 the same law is ever present, as shown in my drawings and 

 diagram. (PI. XX, Figs. 7, 8, 9, 10.) As regards the Sponge 

 a thin membrane overlies the work described, having upon it 

 its spicules lying athwart in the usual orderless arrangement, 

 which distinguishes the genus Hymeniacidon (Bowerbank) to 

 which this is referred. Look where you will, there is not a 



* I have a mounted specimen of the periostraeum which shows every 

 stage of the perforation , and the remarkable sharpness of the cutting, and 

 its strictly mathematical precision defines with accuracy the mode of opera- 

 tion, as it simulates exactly that done by a punch or any other sharp 

 instrument, and this is especially shown when the work is not quite accom- 

 plished, having the same appearances as when a cut through any object ia 

 incomplete. (PI. XXI, Fig. 2.) In no instance is any Sponge present. 



