Fig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
PLATE IV. [Piate 15.] 
SECTION 2.—PTERYGOTUS. 
Plerygotus anglicus. THORACIC AND ABDOMINAL SEGMENTS. 
The third segment of the body, with projecting antero-lateral processes. A specimen 
already figured by Professor Agassiz (l.c.) (Lord Kinnaird’s cabinet.) 
From the slight obliquity of the lateral edges, this is probably the fourth segment. It 
is the largest segment of this species known. Reduced to two-thirds. (Lord 
Kinnaird’s cabinet. ) 
The fifth segment, the ends almost square. (Collection of the Watt Institution, 
Dundee. ) 
The same segment in a young specimen. (Lord Kinnaird’s cabinet.) 
Figs. 5, 6. Probably the under surface of the eighth and ninth segments (see Woodcut 9). 
The posterior segments are more extensively sculptured than the anterior ones, 
especially on the under side. (Lord Kinnaird’s cabinet.) 
From Balruddery Den, Perthshire, in the Basement Beds of the Old Red Sandstone. 
