PLATE XV. 
UPPER SILURIAN CRUSTACEA. 
Order—MEROSTOMATA. 
Sub- Order—HuRYPTERIDA. 
Pterygotus bilobus, var. y, perornatus. 
Fig. 
1. Head and four anterior segments of body of P#. bi/obus, var. y, showing the larval 
eyes (le), the compound eyes (0, v), and tke right swimming-foot (ectognath), still 
attached zm siti. 
2. The greater part of the body of another specimen, having portions of the thoracic and 
the entire series of abdominal somites preserved. 
3. A very beautifully preserved detached lip-plate of Pt. d:lobus, var. y, showing the 
truncated posterior border (a), by which it was attached tothe head. The surface 
is beautifully squamate. 
From the Uppermost Silurian of Lesmahago, Lanarkshire. 
Drawn, of the natural size, from specimens preserved in the British Museum. 
