68 Dr. R. 11. Traquair on Paheozoic Fishes. 



breadth ; one extremity, which we sliall assume to be the 

 posterior, is truncated, making a " side " of 1^% inch in extent, 

 the other (anterior) is not quite perfect, but seems to have 

 been evenly rounded. The surface which is here exhibited 

 is the inner; it is posteriorly nearly flat, being only very 

 gently concave, but in the anterior half it is more hollowed, 

 there being here an oblong depression^ the bottom of which is 

 again slightly convex or raised. On the posterior part slight 

 concentric furrows of growth may be seen. 



The inner surface of the plate is composed of dense lamel- 

 lated tissue, as in other species of the genus, and the vascular 

 structure of the middle layer exhibited in fracture at the 

 anterior part also corresponds, so far as can be ascertained by 

 the use of the lens. A portion of the impression of the outer 

 surface is seen in front, showing that the external ornament 

 consisted of coarse stellated tubercles, which tend to assume an 

 elongated form. The apices of the tubercles are broken off 

 and remain in the matrix of the impression, a small portion of 

 which, magnified five diameters, is shown in tig. 2. 



The specimen figured is in the Weever- Jones Collection, 

 British Museum, no. P. 194. It is believed to be from Here- 

 fordshire or Worcestershire, but the exact locality is unknown. 

 However, there is also a fragment in the collection from 

 Maindee, in Monmouthshire, which apparently belongs to the 

 same species. 



From Goldleps, Monmouthshire, there is also a fragment 

 of a plate of another species, which will be described and 

 figured in my next paper of the present series. 



Protodus scoticus (E, T. Newton). (PI. I. fig. 3.) 



Onychodus scoticus, E. T. Newton, Geol. Mag. (3) vol. ix. 1892, p. ol. 



This specimen, consisting of an antero-posterior row of 

 eight conical, recurved, sharp, two-edged teeth, united by 

 their bases in the form of an arc of a circle, was correctly 

 described by Mr. E. T. Newton, F.R.S.^ six years ago, but 

 T think wrongly attributed by him to the genus Onychodus of 

 Newberry, which is apparently referable to the Crossopterygii. 

 The fractured surfaces of the teeth show that tlieir substance 

 is formed of vascular dentine like those of Selachii, and there 

 is no central pulp-cavity, whereas in Onychodus the dentine 

 is solid and there is a very large pulp-cavity extending almost 

 to the very apex of the tooth. The teeth of Onychodus are 

 also round or oval in transverse section, those of the present 

 specimen have lateral cutting-edges — in fact, each individual 

 tooth in form closely resembles the teeth of Protodus Jexi, a 

 Selachian described from the Lower Devonian of Canada by 



