192 THE HABITAT OF THE EURYPTERIDA 



varied. Traquair, who has made such a careful study of the ich- 



thology of the Old Red Sandstone of Great Britain, has established 



the following fish zones in the Caithness area (272): 



x , „,„ A { Tristichopterus alatus Egert. 

 John O Groats •<,... . . . ,. , . „. ° 



[Microbrachius dicki Iraq. 



[Coccosteus minor H. Miller 

 Thurso -j Thursius pholidotus Traq. 



[Osteolepis microlepidotus Pander 



[Pterichthys, 3 species 

 Achanarras -j Cheirolepis trailli, Ag. 



[Osteolepis macrolepidotus Ag. 

 This fish fauna is very different from that to the south of the 

 Grampians in Forfarshire, there being no species in common between 

 the two areas and only two genera, Mesacanthus and Cephalaspis, 

 the latter being represented in Caithness by only a single specimen. 15 

 From this division no eurypterids have been reported. 



In Caithness and in the Orkneys and Shetland isles has been 

 found a phyllopod crustacean of a genus which at present lives in 

 rivers and freshwater lakes and playas, namely, Estheria. T. Rupert 

 Jones has described the species E. murchisonia, which is abundant in 

 a "dark grey, tough, fine-grained, sandy flagstone, slightly micaceous, 

 somewhat varying in tint and hardness. .... Great num- 

 bers of the valves are spread over large surfaces of the flagstone, some- 

 times scattered sparsely, sometimes congregated in groups, forming 

 films between the layers of fissile stone" (191, 405). Murchison 

 says of this species: "It- occurs in certain localities in such numbers 

 as to form layers an inch or two thick, entirely made up of the thin 

 carapaces" (191, 404). 



The Old Red sandstone of Lome has yielded, besides Pterygotus 

 anglicus remains, two species of chilognathous myriopods, Campecaris 

 forfarensis (Page) and Archidesmus sp. described by Peach (214, 83). 

 These are among the earliest myriopods yet known and suggest that 

 the beds in which they were found were formed on land, for if the 

 myriopods had been transported far they would have been destroyed. 

 Moreover, since they had not hard parts to be preserved, they must 

 have been buried quickly. A playa would be the ideal place for their 

 burial, but I do not know enough about the beds in which they were 

 found to state that they were formed in a playa. Macconochie has 



15 The significance of this fauna has already been discussed in chapter III, p. 02, and the other 

 aspects will be considered below, p. 247, et seq. 



