DEVONIAN FOSSILS. 233 



a great quantity not worth removing. The most remarkable 

 character of these sponges is the thin, very dense, superficial 

 covering to the coarse cellular internal network ; which however 

 might be almost paralleled by a slice of the common large cup- 

 sponge of Ceylon. As so many authorities for whose opinions I 

 entertain a high respect supposed the reticulation to be the can- 

 cellated structure of bone, I thought it due to them, that transpa- 

 rent microscopic sections should be prepared of some of the most 

 bone-like portions and submitted to powerful microscopes, and 

 for this purpose I trespassed on the kindness of my friend 

 J. Carter, Esq., of Petty Cury, Cambridge, who possesses not 

 only an extremely fine microscope, but admirable skill in the use 

 of it and in the preparation of the objects. I have to thank him 

 for not only putting slices of the present fossils under a high 

 power, but making similar slices, for comparison, of fossil bones 

 of various animals and of sponges — the results entirely confirm- 

 ing the opinion I had formed from an examination with my 

 naked eye, namely, that there was no bone- structure whatever 

 in the Cornish fossils ; which indeed was obvious enough to any 

 one reflecting on the way in which bones grow. 



Steganodictyum Cornubicum (M'Coy). 



Sp, Char. Fronds forming large, flat, shghtly undulating ex- 

 pansions, about one line thick, and several inches long and 

 wide, with irregular broad, transverse undulations or impres- 

 sions; the middle supported by a thick, simple, gradually 

 tapering, stem-like portion, which has a thickness and width of 

 about three lines at 4 inches from the apex ; surface of stem and 

 frond, or lateral expansions, generally dark-coloured, dense, 

 and uniformly marked with close, equal, broad, flat, longitu- 

 dinal ridges^ separated by deep sulci only one-fourth or one- 

 third the width of the ridges (about eleven ridges in the space 

 of two lines on all parts of the surface) ; the direction of the 

 ridges is irregular, being sometimes over large spaces perfectly 

 straight and parallel, but more usually much undulated ; under 

 a strong lens the ridges are seen to be punctured by nume- 

 rous minute cell-openings, from one to three irregular rows to 

 each ridge, rather more than their diameter apart ; cell-struc- 

 ture of the interior, coarse, polygonal, averaging six cells in 

 the space of two lines. 



The midrib of this species is often found separated from the 

 thin, foliaceous expansions, and has been then described as Ich- 

 thyodorulites of the genera Onchus, Ctenacanthus and Dipla- 

 canthus. I have however repeatedly noticed its contact with, and 



