PLATE XIII. 
UPPER SILURIAN CRUSTACEA. 
Order—MEROSTOMATA. 
Sub-Order—EvuRYPTERIDA. 
Pterygotus bilobus, var. y, perornatus. 
Fig. 
1 a. An almost entire example, reduced to one half the natural size. 
a,a. The antenne, detached and displaced (the points of attachment to the 
head are marked by stars). 
o, o. The eyes; and (/e) the larval eye-spots or ocelli. 
e. An endognath and part of another, displaced. 
ec. The ectognaths, or swimming-feet; their great basal jomts (¢, ¢) are 
detached, and lie in front of the head. 
m. The metastoma or post-oral plate. 
The telson (20) is restored. 
| 6. The larval eyes, magnified three times. 
1 c. One of the large compound eyes, magnified three times. 
1 d. A portion of same, magnified fifteen times. 
1 e. The metastoma, of the natural size. 
| f. The coxal joint of one of the ectognaths, natural size. 
1 g. Part of a thoracic segment, magnified three times, to show the scale-like markings on 
its upper part. 
1 4. Three of the branchie, magnified three times, seen in this specimen where a portion 
of a thoracic segment has been removed. 
From the Uppermost Silurian of Lesmahago, Lanarkshire. 
Drawn from a specimen in the Museum of Practical Geology, Jermyn Street. 
