4A BRITISH FOSSIL CRUSTACEA. 
these require solid points d’appui. ence, 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.”* In the living Zemulus, 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 Lowrr Oip Rep Sanpstons, 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. 
