CEPHALASPID.13. 



59 



cellular cavities of the margin and of the central part of the shield were only indicated 

 superficially by slight undulations of the tuberculated test. The outer margin of the 

 shield, especially of the cornua, contrary to what is seen in Ccphalaspis, where the inner 

 border of the cornua is denticulate, is furnished with irregularly tooth-like processes of 

 various length. 



General Remarks. — The remains of this beautiful and well-marked little Cephalaspid 

 were described in the ' Silurian System/ and the earlier editions of' Siluria,' from detachcxl 

 specimens of the cornua, as toothed jaws of small ganoid fishes, Pt. {Sclerodas) pustuliferus 

 and mirabilis. In the last edition Sir Roderick rem.arks that Dr. John Ilarley 

 (formerly of Ludlow) had suggested the true nature of these supposed fish-jaws. (See 

 description of PI. XXXV in 'Siluria,' 1867.) At page 241 of the same edition it is 

 stated that Mr. Salter was inclined to regard these cornua as the jaws of Cephalaspis or 

 Pteraspis. The most important feature about Eukeraspis appears to me to be the existence 

 of the remarkable cavities between the two laminae of the shield-test, but unfortunately it 

 is exceedingly difficult to ascertain definitely their structure and relations, on account of 

 the rarity of specimens of the fish, and especially of specimens well preserved. Were it 

 possible to describe these structures with accuracy, their peculiarity, though paralleled 

 by feebly developed marginal cavities in Cephalaspis, would, I think, justify the erection 

 of Eukeraspis into a totally distinct genus. The small vertical breadth of the shield, and 

 the outline of its posterior border, as seen in fig. 13, PI. XIII, renders it improbable that 

 we have in these beautiful little specimens a complete cephalic shield comparable to that 

 of Eucephalaspis, and leads one to suppose that an additional plate such as is presented 

 by Auchenaspis was attached along this border. This is a question Avhich inquiry with 

 the haunner may soon decide ; provisionally, Eukeraspis may remain as a subgenus of 

 Auchenaspis. 



The only specimens yet obtained of this form are from the Downton Sandstone near 

 Ludlow. 



Genus 3. — Didymaspis, Lankester. 

 DiDYMASPis, ZawArs^er. Geol. Mag., vol. iv, p. 152, 1867. 



Derivation. — S/Su/toc, twin; a(T7r<c, a shield. 



Characters. — Scutum in duas partes subajquales divisum, anteriorem semicircularem 

 in qua oculi sunt positi, sine cornibus divergentibus, posteriorem oblongani. 



1. Didymaspis Grindrodi, Lankester. PI. XIII, figs. 1, 2. 



DiDTMASPis Grindrodi, Lankester. Geol. Mag., vol. iv, p. 1.")?, pi. viii, IS67. 

 Name. — In honour of Dr. Grindrod, of ^Malvern. 



