PLATE X. 
UPPER SILURIAN CRUSTACEA. 
Order—M&ROSTOMAYA. 
Sub- Order—EURYPTERIDA. 
Fic. 
1—8. Pterygotus bilobus, Salter, var. a, cnornatus. 
1. Represents an almost entire example, having several of its appendages pre- 
served. 
a, a. The chelate antenne, displaced (the stars indicate the proximal ends). 
o, o. The large compound eyes. 
s, s. The serrated mandibular borders of the basal joints of the maxillipeds or 
ectognaths (their general outline is seen through the carapace). 
ec, ec. The ectognaths, with their broad, oar-like extremities. 
e. One of the small endognaths, preserved entire, but lying on the slab 
detached from the head. 
c. The narrow median lobe of the thoracic plate (the impression seen 
through the overlying somites). 
2. An almost equally well-preserved specimen. ‘The antenne (a, a) are still attached in 
their normal position to the anterior border of the head-shield. One of the 
endognaths (e) and an ectognath (ec) are still 7 sift; the metastonia or post- 
oral plate (7) is clearly seen. 
3. Exhibits well the large compound eyes (0, 0) and the larval eye-spots or ocelli (/e). 
All the appendages have been detached from this specimen, and lie at a little dis- 
tance from it upon the same slab (they are represented in the Woodcut, p. 58). 
N.B.—The small figures placed against the body-segments in all these plates correspond 
throughout with the small Roman numerals placed against the segments of the restored 
figures of Pt. anglicus, given in Part I, Pl. VIII, of this Monograph. 
From the Uppermost Silurian formation of Lesmahago, Lanarkshire. 
Drawn, of the natural size, from specimens in the British Museum. 
