CEPHALASPIDtE. 



4.3 



Bescriptions of Genera and Species. 



Genus 1. — Cephalaspis, Agassiz. Poissons fossilcs, vol. ii, p. 149, 1835. 



Derivation. — Kt<pa\r\, the head ; aairiq, a shield. 

 Characters. — Scutum cephalicum simplex semicirculare. 



The genus Cephalaspis, as here indicated, may be conveniently split into three 

 subgenera. 



1. EucEPHALASPis.' — Scutum postice cornibus lateralibus instructum, in medi(. 

 aliquantb productum. 



2. Hemicyclaspis.2 — Scutum sine cornibus lateralibus : postice subtruncatum. 



3. Zexaspis.' — Scutum Eucephalaspidis scuto simile : scutellum dorsale (vel scutella) 

 post scutum cephalicum positum. 



It seems to be a clearer representation of the relations of these fishes to dissociate the 

 form destitute of cornua, and that with body-plates as well as a cephalic shield, from the 

 other species (which agree in possessing cornua and in other matters very closely), than 

 to leave them all in one group, each being equally designated Cephalaspis. It is quite 

 possible that further research will render it desirable to consider what I have here called 

 sub-genera as genera. Fragmentary remains indicating species belonging to the genus 

 Cephalaspis, or only sufficient to point to the section Osteostraci, and not furnishing 

 evidence of sub-generic detaib wiU be spoken of here as Cephalaspis. 



Such remains occur in the Tiles tones ; in the Ledbury passage-beds we have Hemi- 

 cyclaspis, and in the Cornstones of Herefordshire Zenaspis. Eucephalaspis is found in 

 the Cornstones and the Scotch Lower Old Red. 



1. Eucephalaspis Lyellti, Ayassiz. PI. VIII, fig. 1 ; PI. XI, figs. 1 and 2. 



Cephalaspis Lyellit, Agassi:. Pois. foss., vol. ii, p. 149, pi. 1, fig. 2, 183;'). 

 Name. — Named after Sir Charles Lyell, Bart. 



Slratigraphical Position. — Lower Old Red Sandstone (Scotch area). 



' (i) ; and K«pn\u(jfrii, Cephalaspis. 



- ii^ikvkXkjs, semicircular ; uoTris, a shield. 



^ Zei)», Zrji us, Jove ; aairts, a shield. 



