446 
ELEMENTS OF GEOLOGY. 
The number of species of fish already obtained from the 
middle division of the Old Red Sandstone in Great Britain 
is about 70, and the principal genera, besides Osteolepis and 
Pterichthys^ already mentioned, are Glyptolepis^ Piplacan- 
thus^ Dendfodus^ Coccosteiis^ Cheir acanthus^ and Acanthoides. 
Lower Old Bed Sandstone. —The third or lowest division 
south of the Grampians consists of gray paving-stone and 
roofing-slate, with associated red and gray shales; these 
strata underlie a dense mass of conglomerate. In these gray 
beds several remarkable fish have been found of the genus 
Fig. 502. 
Cb-phalaspis Lyellii, Agass. Length 6f inches. From a specimen in my collection 
found at Glammiss, in Forfarshire. (See other figures, Agassiz, vol. ii., tab. 1 a 
and 1 b.) 
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. b, c. Scales from 
different parts of the body and tail. 
named by Agassiz Cephalaspis^ or buckler-headed,” from 
the extraordinary shield which covers the head (see Fig. 
502), and which has often been naistaken for that of a trilo- 
bite, such as Asaphus, A species of Pteraspis^ of the same 
family, has also been found by the Rev. Hugh Mitchell in 
Fig. 503 . beds of corresponding age in 
Perthshire; and Mr. Powrie 
enumerates no less than five 
genera of the family Acan- 
thodidse, the spines, scales, 
and other remains of which 
have been detected in the 
gray flaggy sandstones.* 
In the same formation at 
Carmylie, in Forfarshire, com¬ 
monly 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 quarry men the ‘‘Seraphim,” from the 
* Powrie, Geol. Quart. Jour., vol. xx., p. 417. 
Pterygotus anglims, Agassiz. Middle por¬ 
tion of tbe back of the head called the 
Seraphim. 
