PLATE II. [PLate 13.] 
SECTION 2.—PTERYGOTUS. 
Fig. 1. Plerygotus acuminatus. Outline of the carapace ; natural size. 
Fig. 1a. The same, reduced nearly one half. 
Fig. 2. The ultimate joint or free ramus of the chela of the antenna of an adult (?) specimen. 
2* A few of the teeth magnified. 
Fig. 3. Penultimate joint or fixed ramus of the chela of an antenna, probably of this species. 
Fig. 4. A metastoma ; a, the median ridge upon its surface. 
Fig. 5. The serrated inner lobe or process of the ectognath. 
Fig. 6. Nearly entire basal joint of the ectognath ; at w, a portion of the sculptured orna- 
mentation, magnified ; co, the point of attachment for the next joint, 4, Fig. 7. 
Fig. 7. Tergal surface (or that part applied against the body) of the ectognath. 
Figs. 8, 9. Sternal or ventral surface of the several joints of its palp. 
co, basal joint (coxognathite). 
4, second joint (basignathite). 
2, third joint (ischyognathite). 
m, fourth joint (merognathite). 
ca, fifth joint (carpognathite). 
P, sixth joint (prognathite). 
@, seventh joint (dactylognathite). 
Fig. 10. The segments of the body of a smaller specimen; the segments a to £ have a small 
double keel, and are probably thoracic ; g, 2, ¢, 4, are probably abdominal rings, 
and are destitute of these ornaments ; the form of the terminal joints e, 7, is shown 
in Fig. 11. 
Fig. 11. Five abdominal rings and the ovate apiculate telson. 
on 
Fig. 12. An abdominal ring of a larger specimen. 12* Its sculpture magnified. 
Fig. 13. The telson or terminal joint. 
All the above are from Lesmahago, Lanarkshire, and are in the Museum of Practical 
Geology. 
