PLATE XII. 
UPPER SILURIAN CRUSTACEA. 
Order—MEROSTOMATA. 
Sub- Order—EHuRYPTERIDA. 
Pterygotus bilobus, var. 8, acidens. 
Fic. 
1 a. Represents an individual of the natural size. 
le. The larval eye-spots. 
0, o. The compound eyes. 
One of the antenne. 
m. ‘Che metastoma, or post-oral plate. 
ec. One of the ectognaths. 
op. The operculum (¢, its central portion). 
ér. Some of the branchiz. 
The segments marked 15 and 16 are absent in the specimen. 
a. 
~ 
1 4. Antenna, magnified twice the natural size ; m, moveable ramus of chela. 
1c. Some of the scale-like markings upon the surface of the thorax, greatly 
magnified. 
1 d. Some of the branchiz, enlarged twice the natural size. 
1 e. Thoracic plate restored (natural size). 
From the Uppermost Silurian of Lesmahago, Lanarkshire. 
Drawn from a specimen in the Museum of Practical Geology, Jermyn Street. 
