70 



Renews — Dr, Traquair on Silurian Fishes. 



While the original conception of the Heterostraci is enlarged in 

 this manner, Ateleaspis seems to form a link between its lowest 

 family (the Coelolepid^) and the order Osteostraci. Dr. Traquair 

 points out that the shape of this organism is like that of Thelodus, 

 while its polygonal plates and scales merely represent groups of the 

 dermal tubercles of the latter fused together by the great develop- 

 ment of their bases. At the same time some of the basal layers of 



Fig. 4. — Drepcmaspis Gmnendenensis, Schliiter. Eestored outline of the dorsal 

 aspect, the surface ornament omitted, and the tail twisted round so as la 

 show the caudal fin in profile, c, central plate ; p.l., postero -lateral plates ; 

 r., rostral plates ; x., orbits? 



the plates contain distinct bone-cells, a peculiarity necessitating the 

 reference of Ateleaspis to the Osteostraci. Dr. Traquair is therefore 

 of opinion that Cope and the British Museum Catalogue are correct 

 in regarding the Heterostraci and Osteostraci as closely related 

 orders, while Professor Lankester is no longer justified in main- 

 taining that "there is absolutely no reason" for grouping them 

 together beyond that they " occur in the same rocks." 



