On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 501 
Polyrhizodus magnus—F. M‘Coy, 1855. “ Brit. Paleoz. Foss.,” p. 641, pl. 3k., figs. 6, 7, 8. 
9 radicans—Morris and Roberts, 1862. “ Quart. Journ. Geol. Soc.,” Vol. XVITI., p. 101. 
2 3 Enniskillen, 1869. ‘Cat. of Type Spec. Foss. Fishes,” p. 7. 
5 Pr Young & Armstrong, 1871. ‘‘ Trans. Geol. Soc., of Glasgow,” Vol. ITI., Supt., 
jo Ub | 
” 2 ean rf 1876. ‘Catal. West. Scot. Foss.,” p. 63. 
re D J.J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 363. 
55 (magnus) yh 1878. ‘5 6 rr p- 363. 
Teeth, when full grown 2°5 in. in breadth and 1°5 in. in height. The erewn ante- 
riorly occupies one-third of the vertical diameter. From the anterior ridge it inclines 
at an angle of 45° backwards and upwards to the crest formed with the posterior sur- 
face. The anterior coronal surface is smooth, slightly polished, and convex ; it is 
-75 of an inch across the centre, from which the crest and anterior ridge converge 
towards each lateral extremity, and terminate in an acute angle. From the raised 
surface forming the centre of the tooth it is depressed laterally, and towards each 
end is considerably bent downwards and backwards, so as to combine to form the 
posterior median ridge. The anterior ridge dividing the crown from the root is 
plain, and without folds or strize ; beneath the ridge the surface of the tooth retreats 
almost at a right angle to the crown, with slight vertical plications towards the 
base of the radicles. Posterior surface of the crown 1:0 inch across the central 
portion ; vertically the section is concave; but laterally the surface forms a nearly- 
straight line. It is ovoid in form, converging laterally to an acute angle. Lower 
surface bounded by the posterior ridge °2 of an inch wide, and consisting of three 
or four imbricating parallel folds. The ridge is considerably elevated, and a deep 
groove extends beneath it and the base of the root. 
Root, thicker than the upper part, its depth equalling one-third that of the 
entire tooth. It is divided into twelve or fourteen thin plate-like radicles, deeply 
cleft and usually separated by an indentation equal to their own diameter. There 
are generally instances in each tooth in which two of the rootlets have coalesced 
and form one thick, almost square fang. 
Prof, M‘Coy has described and figured this species in his work on “ British 
Paleozoic Fossils.” The specimens at his disposal appear to have been smaller than 
those now figured from the cabinet of the Earl of Enniskillen, but otherwise the types 
agree. A slight discrepancy between M‘Coy’s description and the plate occurs. 
In the text it is stated that the number of rootlets is six or eight, whilst im the 
figure thirteen are represented. The latter is, no doubt, the correct number. 
A considerable variety in the details may be observed in the large series of this 
species collected from the Limestones of Armagh, and at present in the Enniskillen 
collection. Full-grown teeth are generally more or less worn on the surface, 
especially in the centre, considerable variety exists in the form of the teeth, in the 
thickness and the relative size of the crown and the base. The specimens vary ix 
