﻿44 BRITISH FOSSIL CRUSTACEA. 



these require solid points d'appui. Hence, we may conclude that the integument of the 

 Pterygotus, thin and fragile as are its remains, possessed a great amount of firmness in 

 the recent state." 1 In the living Limulus, the shell is equally thin to that of the fossil 

 Pterygotus, but this leathery integument nevertheless affords attachment to very powerful 

 muscles. 



Distribution. — This species is peculiar to the Lower Old Red Sandstone, and has 

 been obtained at Balruddery, Perthshire ; at Leysmill near Arbroath, at the quarries of 

 the Turin Hills, near Reswallie, at Tealing and Carmyllie, and other places in Forfarshire. 



The specimens figured are from the collections of Lady Kinnaird, James Powrie, Esq., 

 the British Museum, and the Watt Institution, Dundee. 



1 'Mem. Geol. Surv.,' Mon. I, p. 36. 



