PLATE XX. 



Fig. 



1. Pterichthys Miller i, from a specimen from Lethen Bar in the British Museum 



(49191). Here the plates of the ventral surface of the carapace are seen 

 from their inner surfaces. 



2. A specimen from the same locality, showing the greater part of the body- 



carapace from the dorsal aspect, part of the left pectoral appendage, the 

 dorsal fin, and the heterocercal caudal with indication of the fin-membrane; 

 natural size. From a specimen in the Williamson Collection, Manchester 

 Museum. 



3. Central part of the head of a specimen from the same locality, in the British 



Museum (49187), showing the orbit, with remains of the median and ocular 

 plates. Natural size. 



4. Anterior median dorsal plate, with deficient margins, but showing the external 



sculpture. From Cromarty, in the Hugh Miller Collection, Royal Scottish 

 Museum. Natural size. 



5. Posterior ventro-lateral plate, with part of the bony matter preserved and 



showing the external sculpture. Also from Cromarty, in the Hugh Miller 

 Collection, Royal Scottish Museum. Natural size. 



