494 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
riviale, P. levissimus, given by Prof. Agassiz to teeth of Petalodus which he at 
one time considered distinct from P. hastingsie, further observation, however, con-- 
vineed that learned ichthyologist that they were modifications only of the same 
species, 
The teeth vary considerably in detail as to form, and occasionally examples are 
discovered which appear to be considerably distorted, as in Pl. LIX., figs, 18, 20, in 
which the root is deflected entirely to one side. These examples may have occupied a 
position towards the posterior extremity of the jaw. 
Formation and locality : Mountain Limestone, Armagh. 
He coll, Karl of Enniskillen. 
Petalodus acuminatus, Agassiz. 
(Pl. LIX., figs. 22-24.) 
Chomatodus acuminatus—L. Agassiz, 1833. “Rech. sur les Poiss. Foss.,” Vol. III., p. 108, 
pl axe fios I ONS! 
Petalodus acuminatus— % 1840. “ Rech. sur les Poiss. Foss.” Vol. III, pp. 174 
and 384. 
a 33 J. E. Portlock, 1843. “Geol. of Londonderry,” p. 461. 
~ » C. G. Giebel, 1843. ‘Fauna der Vorwelt,” Vol. L., pt. iii, p. 345. 
s 9 H. G. Bronn, 1848. “Nomencl. Paleont.,” p. 949. 
A rhombus— F. M‘Ooy, 1848. “Ann. and Mag. of Nat. Hist.,” 2nd ser., Vol.. 
IT.; p. 125. 
»,  acuminatus—H. G. Bronn, 1849. ‘ Enumerator Paleont.,” p. 646. 
“5 J. Morris, 1854. “Catal. Brit. Foss.,” p. 337. 
3 s F. J. Pictet, 1854. “Traité de Paléont.,” Vol. II., p. 271. 
oa . F. M‘Coy, 1855. “ Brit. Paleozoic. Foss.,” p. 635, pl. iii. G, fig. 4.. 
Ss rhombus, a 1855. re . 5 p- 635. 
5 acuminatus—Morris and Roberts, 1862. ‘Quart. Jour. Geol. Soc.,” Vol: XVIITI., p. 101. 
% 3 J.J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 361. 
Teeth, “Crown sharp, compressed, anterior face of variable height, regularly 
rhombic, the upper and lower margins sometimes symmetrical, the lateral portions. 
of each being nearly straight, or slightly arched downwards, and meeting in the 
middle at an obtuse angle, or, more frequently, the angle both of the apex and 
coronal ridge more or less rounded. The cutting edge is obscurely undulato-dentate 
in some specimens by short obsolete vertical furrows, and minutely crenulato- 
striated, more commonly without the vertical plice, from the faint undulations of 
the edges. The lower margin is prominent, and surrounded by five or six small 
imbrications of ganoine. These descend lower (as usual) on the posterior face, 
where also the mesial angulation is less ; surface smooth, with a few fine irregular 
longitudinal strize ; root moderately large.” Height of the middle of the crown ‘9 
of an inch; width of crown 1°5 inch; depth of root 1:2 inch. ‘The proportional. 
height and size of the crown compared with that of the root is very variable. 
