274 The American Geologist. xnvembci-. 1902 
verse muscles in specimens of the remarkable cladodont sharks 
(Clodoselachc). 
The strikingly preserved tissue in these specimens had long 
been known to the present writer ; but it was only recentlv, wdiile 
re-examining the structures of cladoselachids, that he caused 
favorable fragments of it to l)e microsectioncd. The material 
was then found so well preserved that he was led to prepare 
the following notes upon it, illustrated by photomicrographs. 
The latter were taken by his colleague. Dr. Edward Learning, 
to whose generous aid, — in this as in similar instances, — the 
writer is greatly indebted. 
It may be said, in passing, that the specimens of Cladose- 
lache referred to by Newberr}' are of exceptional value to one 
who is studying fossilization as well as palaeanatomy ; thus in 
the type of C. kepleri, gill filaments are reproduced distinctly ; 
and in several specimens the mineralized muscle bands, some- 
times in patches several inches in length, are so well preserved 
that they suggest in color, distinctness and texture, the mummi- 
fied tissue of recent fish. PI. VIII. Fig. i.'" 
The general appearance of the fossil muscle fibres is well 
shown in PI. \TII, Fig. 2. from a photograph taken under a 
low power. (Jne notes the crowded mass of cylindrical fibres 
whose outlines, in many cases clean-cut, suggest that the tissue 
at the time of its fossilization could not have been badlv de- 
composed. Indeed, judging from PI. IX, Fig. 3, in which a 
similar section is magnified about 1,000 diameters, one can 
conclude that the tissue was even in a very fair state of pre- 
servation, for, considering especially the fact that the fibres 
have undergone mineralization, the striae are still undistorted, 
and even what can reasonably be interpreted as bits of the sar- 
colemma ( at the j^oint '^ and * ) are reproduced. These ancient 
luuscle fibres, in fact, preserve the contours better, as it hap- 
pens, than the fibres in recent tissue in the adjacent photo- 
graph, PI. IX, iMg. 4, taken from a well preserved specimen 
of Heferodoiitns. 
Comparing further the preparations (both magnified equal- 
ly) of the Devonian and of the recent shark, we cannot fail to 
note the greater coarseness of the transverse striae in the ancient 
*In the present figure (from a specimen of C. fyleri) there is shown 
also a portion of the characteristic Cladoselachian (pectoral) fin. Its 
web can be traced oack along the side of the trunk in the hue indicated 
by dots. 
