BRITISH FOSSILS. 



49 



show what was their original position). 

 is distinctly shown in this specimen. 



The shape of the carapace 



FIG. 3. 



U 



P. perornatus, carapace, and swimming feet ; one-third natural size. 



Locality. Lesmahago, Lanarkshire, with the last. Besides the 

 Pterygotus acuminatus, Plate II., this is the only large species 

 which occurs in the locality. It is not common. Mus. Pract. 

 Geology. Collected by Mr. R. Slimon. 



P. perornatus, Yar. plicatissimus, Plate I. fig. 1 6. 



This, which differs materially in the breadth of the segments, and 

 somewhat also in the manner of sculpture, must be regarded, till 

 more specimens are obtained, only as a variety. But it will very 

 probably be found a distinct species, in which case it is only 

 necessary to use the varietal name as a specific one. 



The carapace (in fig. 1 6) is much compressed longitudinally, but 



the true form would probably be a full semioval, as in the preceding 

 woodcut ; the position of the eyes is obscurely marked. The sur- 



[1.] D 



