REPORT ON FOSSIL FISHES. 19 
Rhizodus Hibberti (ib. p. 612), he has given Holoptychius Portlochtt with an 
appended query. 
But an examination of the originals of Col. Porttock’s figures from Mag- 
hera, Derry, now in the Museum of Practical Geology, Jermyn Street, reveals 
the unquestionable fact that they are not specifically identical with Rhizodus 
Hibberti, nor even generically, if the usual ideas as to the definition of Rhizodus 
are to be retained. The teeth are rounded or oval in transverse section, and 
devoid of the cutting edges characteristic of Rhizodus; the folds of the base 
are proportionally large and coarse, and the surface is covered with close and 
minute yet sharp vertical striz, which fade away towards the apex as well as 
along the anterior aspect of the tooth. Now these are precisely the main 
external characters of the teeth from the Coal Measures first named by 
Messrs Hancock and ArtHEy Archichthys sulcidens,* and accordingly I have 
already (Proc. Roy. Soc. Edin. ix. 1878, p. 657) proposed to transfer 
“ Portlockit” to the last named genus. 
From Tweeden Burn, Liddisdale, there are two teeth which I cannot 
distinguish in essential characters from those of Archichthys Portlockii of the 
Irish Lower Carboniferous rocks. Of these the larger is broken, both at base 
and apex, but when entire would I think have measured 13 inches in height. 
The transverse section is rounded; the base displays remains of coarse 
plications ; the greater part of the surface as shown in the specimen is smooth, 
but the posterior aspect is strongly marked with the characteristic delicate 
striation. The other is half an inch in height by 3; inch in long diameter at 
the base, which also shows remains of coarse plications ; the transverse section 
is rounded, and the characteristic strize extend over a proportionally larger 
extent of the surface than in the larger specimen. In fact, this smaller tooth is 
nearly the exact counterpart of one from Maghera in the Jermyn Street 
collection. 
Associated with these teeth are numerous thin rounded scales, which 
probably belonged to the same fish, and which also, though smaller in size, 
closely resemble those of Archichthys Portlockii from Maghera. All of these 
have the outer surface attached to the matrix, and concealed, the inferior surface 
alone being exposed. But one scale from Tarras Water, Eskdale, shows some 
patches of the outer surface, and this is covered with minute granules arranged — 
in closely set lines radiating from the centre. This scale I am also inclined to 
refer to Archichthys Portlockit. 
I have as yet seen no evidence that any of the Rhizodont scales from either 
Liddesdale or Eskdale belong to Rhizodus, and undoubtedly no tooth referable 
to that genus has occurred. 
* “Note on an undescribed Fossil Fish from the Newsham Coal-shale near Newcastle-on-Tyne.”— 
Nat. Hist. Trans. Northumb. and Durham, vol. iv. 1871, pp. 199-201. 
