PLATE Xi: 
UPPER SILURIAN CRUSTACEA. 
Order —MEROSTOMATA. 
Sub- Order —EvRYPTERIDA. 
Fig. 
1. Pterygotus bilobus, var. y, perornatus. 
1 a. Head, with the great maxillipeds or ectognaths still attached, but displaced outwards 
on either side. 
The form of the head-shield, the compound facetted eyes (0,0), and the larval 
eyes (/e) are well seen. The joints of the ectognaths are lettered to cor- 
respond with the names given to the articuli (see page 6, Part I). 
1 4. Facets of eye, magnified ten times. 
1 c. Facets of eye, magnified six times. 
(The form is evidently altered by compression.) 
1 d. Scale-like markings from the right coxal jomt, magnified four times. 
(The upper portion of the left coxal joint is restored.) 
2. A detached lip-plate, showing the lower edge (near the figure 2) to be truncated. (See 
also Pl. XV, fig. 3.) 
3. ‘Two beautifully preserved endognaths, found detached (the joints are lettered as in 
fig. 1). 
From the Uppermost Silurian of Lesmahago, Lanarkshire. 
Figs. 1 a, 2, and 3 are drawn, of the natural size, from specimens preserved in the 
Museum of Practical Geology, Jermyn Street. 
