214 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
Locality—Lesmahago, Lanarkshire, with the last. Besides the 
Prerygotus acumtnatus, Plate II. [Plate 13], 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, Var. plicatissimus, Plate 1. [Plate 12] fig. 16. 
This, which differs materially in the breadth of the segments, and 
somewhat also in the manner of sculpture, must be regarded, till 
Fic. 3. 
P. perornatius, carapace, and swimming feet ; one-third natural size. 
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. 16) is much compressed longitudinally, but 
the true form would probably be a full semioval, as in the preceding 
FIG. 4. 
Plerygotus perornatus, Vax. plicatissimus ; 3rd segment. From the specimen figured in: 
PL. I. fig. 16 ; natural size. 
woodcut ; the position of the eyes is obscurely marked. The surface 
is covered with semicircular plicae, the curves of which open backwards 
(contrary to the usual position over the rest of the body). 
In front is seen the impression of the large ovate median lobe (a) 
