PLATE V. [Pate 16.] 
SECTION 2.—PTER YGOTUS. 
Plerygotus angltcus. POSTERIOR BODY SEGMENTS. 
Fig. 1. Probably the under side of the tenth segment. It is much narrower in proportion to 
its length than the anterior segments. (Lord Kinnaird’s cabinet.) 
Fig. 2. Oblique view of a ring distorted by pressure in a longitudinal direction. 
Fig. 3a. A tergal view of the eleventh or penultimate segment, showing its continuous central 
keel. (Lord Kinnaird’s cabinet.) 
Fig. 3b. Sternal or ventral view of the same specimen, showing a short central ornamented 
(anal?) keel. The specimen is much compressed, but is nevertheless convex on 
both sides. 
Fig. 4. An intaglio in sandstone exhibiting the ventral surface of a more perfect specimen ; 
three-fourths of the natural size. (Watt Institution, Dundee.) 
Fig. 5. The twelfth segment (telson), tergal side, showing the central keel. (Watt Insti- 
tution. ) 
Fig. 6. The sternal surface of a large telson; two-thirds natural size. 
All from the Basement Beds of the Old Red Sandstone, Perth and Forfarshire. 
