Pisces. | UPPER PALAXOZOIC VERTEBRATA, 641 
very slightly oblique to the median line, and not separated by a concavity from the adjoining broad convexity, 
which occupies two-thirds of the tooth, the anterior third flattened, abruptly narrowed, and obliquely pointed 
nearly at right angles. Surface in parts coarsely granulo-punctate, and marked with numerous, obscure, 
longitudinal, arched sulci, parallel to the convex inner margin. Length of rather small specimen seven lines, 
greatest width six lines. 
As I have mentioned before, I think the P. parallelus will ultimately prove to be the middle tooth of this 
species. Our figures of very large anterior teeth, Pl. 3. I. fig. 7, 8, are not quite complete at the anterior 
ends, forming the upper parts of the figure, which in perfect specimens I have since seen is a little longer, 
abruptly narrowed, and marked with angulated obscure sulci of growth. 
Position and Locality—Not uncommon in the carboniferous limestone of Armagh. 
Lixplanation of Figures.—P1. 3. 1. fig.’7. Anterior right tooth, natural size, the upper end when perfect 
is a little longer and narrower; fig. 7 a, profile of ditto partially shewing the inrollment of the outer margin, 
apex imperfect; fig. 8, same tooth of left side; fig. 8a, fore-shortened end view of last specimen; fig. 9, 
posterior terminal tooth, left side. 
Genus. POLYRHIZODUS (A/°Coy). 
Ref—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 125. 
Gen. Char.—Tooth thick, crown but slightly elevated, forming a transversely oval crushing surface, 
narrowing towards the extremities; anterior and posterior ridges separating the crown from the root, obtuse, 
without imbricating folds, the posterior ridge much lower than the anterior; root very large, deeply divided 
into several distinct, root-like lobes, or fangs. 
This is perhaps the most remarkable genus of ichthyolites yet made known, as it presents the only 
instance in the entire class of a fish-tooth divided into several distinct fangs; the imperfectly double, divari- 
cating base of certain sharks’ teeth, or the prolonged external plice of certain sauroids ({oloptychius, Rhi- 
zodus, &c.) not deserving to be viewed in the light of really divided or fanged roots, as in the mammals and 
the present genus of fish. The group is most allied to Petalodus (Owen), with which Agassiz seems to have 
confounded one of the species; but instead of the thin, scale-like or petal-like character of the Petalodi, 
with their highly elevated, compressed, sharp-edged crown, we have a tooth of remarkably thick and clumsy 
form, with the crown but little raised and all the parts obtuse; the crown in Pefalodus is covered with a 
thick coat of smooth, highly polished, enamel-like substance or ganoine, and separated on each side from 
the root by several imbricating folds, while the crown in the present genus is nearly as dull as the root, 
and in one species coarsely punctured as in Psammodus, and the characteristic basal imbrications are replaced 
by a simple, obtuse ridge; finally, in Petalodus, the root forms a large, simple, compressed, truncated base, 
while in Polyrhizodus it is divided into from five to eight fangs. 
PoLtyruizopus MAGNUS (J/‘Coy). PI. 3. K. figs. 6, 7, 8. 
Ref —M ‘Coy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 126.= Petalodus radicans (Ag. MSS, names in 
collections). 
Dese.—Tooth from one-half to two inches wide, and about one inch in depth; crown from three to four 
lines wide, nearly flat, inclining at an angle of about 70° from the slightly raised posterior edge, smooth, or 
with minute branching striz on the upper edge; anterior and upper margins nearly parallel for the middle 
half of the width, while they rapidly converge in the two outer fourths, so that the extremities are narrowed 
to a point at each end, and considerably bent downwards; root very thick and deeply divided into six or eight 
long, ovate, fang-like lobes, roughened by the passage of the nutrient vessels; inferior posterior ridge is (like 
the anterior margin of the crown) simply rounded, without imbricating folds, and about one-third more than 
the width of the crown below the cutting edge. 
Position and Locality.—This fine species is not uncommon in the lower carboniferous limestone of Armagh, 
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