Ch. XXVI.] 



OLD RED SANDSTONE. 



C. [Tahle^ p. 412). — The third or lowest division south of the Gram- 

 pians consists of gray paving-stone and roofing-slate, with associated red 

 and gray shales ; these strata underhe a dense mass of conglomerate. In 

 these gray beds several remarkable fish have been found of the genus 

 named by Agassiz Cephcdaspis, or " buckler-headed," from the extraor- 

 dinary shield which covers the head (see fig. 541), and which has often 

 been mistaken for that of a trilobite, such as Asaphus. 



Fig. 541. 



> 



CepTialaspis Lyellii, Agass. Length 6J inches. 

 From a specimen in my collection found at Glammiss, in Forfarsliire ; see other figures, 



Agassiz, vol. ii. tab. 1 a, and 1 &. 

 a. One of the peculiar scales with -which the head is covered when perfect. These scales 



are generally removed, as in the specimen above figured. 

 &, c. Scales from "different parts of the body and tail. 



In the same rock at Carmylie, in Forfarshire, commonly known as the 

 Arbroath paving-stone, fragments of a huge crustacean have been met 

 with from time to time. They are called by the Scotch quarrymen the 

 " Seraphim," from the wing-like form and feather-like ornament of the 

 hinder part of the head, the part most usually met with. Agassiz, having 



Fig. 542. 



Portions of the Pterygotus anglicu-% Agassiz. 



1. Middle portion of the " Seraphim" or back of the head, with the scale-like sculpturing. 



2. Portion of ihe dilated base of cue of the anterior feet, with its strong spines or teeth, 



used as masticating organs. 

 8. The proximal portion of one of the great anterior claws. 



4. Terminntion of the same, M'iih the serrated pincers. (See Asass. Poiss. Foss. du Yieux 

 Gres Eouge. plate A.) 



1 and 2 are of the natural size ; 3 and 4 are reduced one half. 



