154 



Dr. R. II. Traquair — On Drepanasjns. 



surface is formed by small polygonal plates, remincling us of th& 

 tesselated surface of many Psaramostean shields, while we sometimes 

 find a few larger rostral ones (r.) just at the anterior margin ; and 

 external to these just at the edge of the carapace we find a plate 

 showing a small round depression or pit (x.) which in my Silurian 

 memoir I have supposed might possibly represent an orbit. But to 

 this I shall again refer further on. 



Fig. 1. — Brcpanaspis Gmilndenensis, Schliiter ; i-estored oiitliue of the dorsal aspect, 

 the surface ornament omitted, and the tail twisted round so as to show the 

 caudal fin in profile, m.d. median dorsal plate ; p. I. postero-lateral plates; 

 r. rostral plates ; x. sensory plate. Slightly altered from the figure previously 

 given. 



The surface ornament of all these plates consists of small and 

 tolerably closely set stellate tubercles, and it is to be noted that 

 on the small polygonal ones we often find a tubercle of lai-ger 

 size at or near the centre, as is commonly the case on the polygonal 

 areas of Psammosteus Taylori. 



The tail, springing from the middle of the posterior margin of 

 the carapace, is comparatively short, and terminates in a heterocercal 



