DESCRIPTION OF THE SPECIES OF PTERYGOTUS 231 
1st Segment—This appears to be wanting both in the Tealing 
specimen, and in the specimens figured in Plate IV. [Plate 15]. It 
was, probably, narrower than all the rest and had the outer posterior 
angle much rounded off. 
2nd Segment (woodcut, No. g).—This is five times as wide as 
long, somewhat arched in the middle, and much bent forward at the 
Fic. 9. 
Pterygotus anglicus, from the second to the ninth body ring ; one-fifth the natural size. 
Lowest beds of Old Red Sandstone, Tealing, Dundee. This specimen is in the Museum 
of the Watt Institution, Dundee. 
sides, with indications of lateral processes a, 4, similar to those in 
the third segment. The lateral edges are very oblique : forming an 
angle of about 70° with the posterior edge. . 
3rd Segment, Plate VI. [Plate 17] fig. 1. — This is Agassiz’s 
figured specimen in his Table A, upper right-hand figure. It is four 
and a half times as wide as long, our largest specimen above ten 
inches wide. The posterior angles are rounded off, the anterior 
