Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
. 6. An antenna; the stem which supports the chela is broken, and its joints are not 
Fig. 
Fig. 
Fig. 
PLATE I. [PLate 12.] 
SecTIon IL.—ZRETTOPTERUS. 
1. Plerygotus bélobus more than half grown; showing the epistoma uw, antennz 4, 
endognathary palpi c, contour of the metastoma d, and the ectognath or swimming 
foot. 
ta. Outline of the metastoma and the adjacent parts of the same specimen. 
2. A rather larger specimen ; the parts of the head crushed and confused. 
2a. The sculpture of body rings enlarged. 
3. Anterior portion of one of the largest individuals; the antenne are directed 
forwards ; the swimming feet (ectognaths) 2 sz¢z, with their large basal lobes 4. 
4. A cast of the sternal side of the carapace, with the basal joints of the ectognaths in 
place ; the large eyes are impressed on the lower surface at c. 
4d. The surface of the eyes magnified. 
5. A lateral view of the same carapace. 
clearly distinguishable. 
. 7. A large antenna (belonging to an individual of different sex ?); 4, the long second 
joint ; c, the fixed ramus of the chela; d, the terminal or free claw. 
. 8. An ectognath or swimming foot, forming one of the same group of appendages from 
which Fig. 6 is taken ; co, the large basal joint (coxognathite). See p. 208. 
. 8a. The palp of the same limb magnified; 4, the second joint; z, third; m, fourth ; 
ca, fifth joint (carpognathite), forming in this species the angle of the limb ; this or 
the preceding joint gives origin to the long stylet ¢; 4, the sixth or penultimate 
joint (prognathite) ; @, the terminal joint (dactylognathite). 
9. A carapace, with the swimming feet in place ; part of the upper surface is removed. 
. 10. A metastoma or post-oral plate. 1oa. A magnified view of part of its surface. 
. 11. The telson or terminal segment of the body, compressed laterally. 
. 12. A telson, shortened by pressure in an opposite direction. 
. 13. Plerygolus perornatus ; carapace and six anterior segments of the body ; at 6, the 
fulcral points are seen ; ¢, the rounded posterior edges of the first segment ; d, its 
anterior processes. 
. 13*. An ectognath or swimming foot ; the several joints marked as in Fig. 8a; for the 
figure of a better specimen, see Woodcut 3, p. 214. 
. 14. A basal joint of an ectognath, from the same specimen as Fig. 13%; c, point of 
attachment of the remaining joints. 
. 15. A metastoma. 
. 15a. Its sculpture enlarged. 
. 16. Plerygotus perornatus, var. plicatésstmus ; carapace, much compressed, and partly 
broken away, showing what are perhaps the traces of the impressions of muscles 
(for the ectognaths ?) at 4; a is the central lobe of the epistoma; c, first body 
segment. 
16a. The ornamentation of the carapace, magnified. 
17. Eurypterus lanceolatus, without the carapace, but with the ectognaths or swimming 
feet in place. 
17*. Sculpture, magnified. 
The above are from the Uppermost Ludlow Rocks, Lesmahago, Lanarkshire, and are in 
the collection of the Museum of Practical Geology. 
The Figures in these Plates are of the Natural Size, unless it be otherwise stated. 
