Pisces. | UPPER PALAZOZOIC VERTEBRATA. 617 
This little species is something the size and shape of the foot of our common frog, whence the specific 
name. 
Position and Locality.—Rare in the black shaly beds of the carboniferous limestone of Derbyshire. 
Explanation of Figures—PI. 3. G. fig. 9, natural size; fig. 9 a, ditto magnified. 
Genus. CHOMATODUS (4g.) 
Gen. Char.—Teeth transversely elongate, oblong, compressed; base of the crown encircled with several 
narrow imbricating folds of ganoine, descending lower on the inner than on the outer side; root also compressed 
in the same direction as the crown. 
This genus has, I think, no claims to be retained: the blunt-coned, thick species (as C. cinctus, &c.) 
might be advantageously classed with Helodus, most of the species of which, with the same form and punc- 
tured surface, have more or less perfectly developed imbricating folds at the base of the crown; and the thin, 
unpunctured species with a cutting edge belong to Petalodus (Owen), in which the folds always exist. I use 
the genus here for some intermediate types provisionally, and for Agassiz’ species. 
The genus is only at present known in carboniferous rocks. 
Cuomatopus (HELopUS) cIncTUS (Ag.) 
Ref —Ag. Poiss. Foss., Vol. III. t. 15. f.18 and 21. 
Desc.—Elongate, oval, or sub-rhomboidal, moderately convex on the sides; an obtusely rounded prominence 
nearly in the middle of the crown, but usually closer to one of the sides than the other, the surface between 
them forming in that case a nearly vertical area; surface poroso-granular, margin of the crown surrounded 
by a variable number of fine flexuous wrinkles, most numerous on the narrow ends. Average length of 
rather small specimens about seven lines, width five lines, height three lines. 
Position and Locality.—Not uncommon in the carboniferous limestone of Belsey, Northumberland. 
CHomAtopuS cLAvATUS (J/°Coy). Pl. 3. K. fig. 10. 
Ref—MCoy, Ann. Nat. Hist. 2nd Series, Vol. II. 
Desc.—Tooth clavate, moderately compressed ; crown obtusely rounded at upper edge, and depressed or 
moderately conyex exteriorly, the grinding surface marked under the lens with a very minute vermicular granu- 
lation, coarser near the edge; the imbricating bands separating the crown from the root on the outer side 
numerous (six or seven), undulating, and punctured on their edges, but so minute as to require the lens for 
their perception ; root hard, polished, abruptly narrowed and flattened, nearly smooth ; profile of front sigmoidally 
rounded. Inner side of the tooth concave from the upper edge to the very prominent ridge separating the 
crown from the root, which ridge is placed about half the width of the crown below the cutting edge. Length 
six lines, width six and half lines, from cutting edge to coronal ridge on outer face one and half lines, on inner 
face two lines. 
The clayate form and peculiar sculpturing of the crown easily distinguish this from others of the genus ; the 
only near ally is the C. truncatus, which is parallel-sided, not clavate, has strong simple coronal bands, &c. 
Position and Locality—V ery rare in carboniferous limestone of Armagh. One specimen in the University 
Collection, and another in that of Capt. Jones. 
Explanation of Figures.—PI. 3. K. fig. 10, front view of average tooth (slightly imperfect on one side) ; 
fig. 10 a, ditto profile shewing the coronal ridge at a low level on the posterior side; fig. 104, ditto portion of 
crown magnified. 
4x2 
