144 PALEONTOLOGY. 



P. Egerton. The jaws are small, and possess confluent 

 denticles. 



The type-species is the Ptericlithys Milleri ; others have 

 been based upon proportions of the cuirass, of the pectorals, 

 and the tail ; all are from the " old red sandstone," and the 

 great majority have been found in the Devonian strata of 

 Caithness, and other Scotch localities. 



Genus Cephalaspis (k&phale, head ; asjns, buckler). — In this 

 genus the posterior angles of the shield-shaped helmet are 

 produced backward in a pointed form, giving to the head the 

 form of a " saddler's knife ;" in other respects the genus closely 

 resembles Ptericlithys. 



Mr. D. Page has recently acquired specimens of Cepha- 

 laspis from Lanarkshire tile-stones, forming the base of the 

 Devonian system, which shew a dorsal fin, pectoral fins, and 

 a large heterocercal fin, besides a well-marked capsule of 

 the eye-ball. Cephalaspis Murchisoni occurs in the passage 

 beds from the Silurian to the Devonian systems. 



Genus Pteraspis. — The buckler of Pteraspis truncatus has 

 been found in a Silurian stratum below the Ludlow bone bed ; 

 it is the earliest known indication of a vertebrate animal. 

 Pteraspis Lloyclii occurs in the lower " old red" of Britain. 

 The Palceo- or Archceo-teuthis of Ferd. Eoemer is founded on 

 the buckler of a " devonian " Pteraspis. 



Genus Coccosteus (JcokJeos, berry ; osteon, bone). — If a 

 heterocercal fin were added in outline to the restoration of 

 the fish of this genus (fig. 61), a correct idea would be given 

 of the "old red" fossil, which, in the progress of its recon- 

 struction, has suggested such diverse notions of its nature 

 and affinities. 



The helmet and cuirass are firmly united, and there is 

 no trace of the jointed appendages, like pectoral fins, which 

 characterize Pterichthys. The unprotected part of the trunk 

 shews an ossification of the neural and haemal spines, and of 



