50 



OLD RED SANDSTONE FISHES. 



and a few specimens of a larger Cephalaspis. The specimens are much carbonized and 

 quite black, showing, however, the surface-markings and the scales in parts with a 

 distinctness which varies in specimens and is liable to diminish by exposure after the 

 exhumation. 



There is a fact of interest with regard to the position assumed by the specimens in 

 the rock. They are all very much flattened, but many have apparently also burst 

 along the ventral line, so that the fossil presents the two rows of large flank scales spread 

 out on each side of the dorsal series. This indicates great toughness in the tegumentary 

 skeleton, and implies that the scales were held together by a very strong matrix of fibrous 

 tissue, which was less firm along the ventral surface than in other parts. It has been 

 suggested, as before noted (page 42), that the ventral part, if not the whole of the Cepha- 

 laspids, was covered and firmly connected through the aponeurotic scales with a skin 

 containing small shagreen-like ossicles in parts. The continuity presented by the scales 

 when crushed, as in the specimens of C. Pagci, favours this notion. In the Heterostraci 

 it is clear, from the gland-pits, that there was a considerable development of the parts 

 superficial to the calcified layers of the integument. 



5. EUCEPHALASPIS ASPER. PI. X, fig. 5. 



Name. — From the pointed spinets which exist on the scales and rim of the cephalic 

 shield. 



Characters and General Remarks. — The specimen figured, which is from a nodule in the 

 Lower Old Red Sandstone of Perthshire, and another from the bed in Reswallie, Eorfar, 

 which furnished Mr. Powric with C. Pagei and others of his valuable discoveries, present 

 conoid or dentate spinets (fig. 23) situated on the marginal rim of the head-shield, being 



modified tubercles, and also on the scales, as seen in the figure. How far this structure 

 is sufficient to characterise a species may very well be held to be doubtful, since such 



Fia. 23. 



Spinets from the margin of the shield of Eucephalaspis aspor. 



