636 BRITISH PALZZOZOIC FOSSILS. [ Pisces. 
The P. levissimus and P. Hastingsii as admitted in Agassiz list are the smooth and striated states 
above alluded to of this species, and which states I am absolutely certain may be found in different parts of 
the one tooth, and indicate no specific difference. Col. Portlock’s figure of P. Hastingsii does not, I think, 
represent that species, but more probably the P. acwminatus. 
Position and Locality—Not uncommon in the carboniferous limestone of Armagh; very rare in the car- 
boniferous limestone of Lowick. 
PETALODUS PSITTACINUS (4g.) name only. PI. 3. I. fig. 4. 
Desc.—Root very large, cylindrical, coarsely osseous, one half deeper than the crown is high; crown semi- 
conical, very convex, highly polished, rapidly tapering to a point, which when worn is marked with fine notched 
striz ; base of the crown with about three strong imbricating folds of ganoine. Average height of crown six 
lines ; width at base seven lines ; antero-posterior thickness three lines. 
The thick conical pointed form of the crown of this tooth easily distinguishes it from all others. When 
greatly worn the upper edge becomes obscurely tricuspid, and coarsely striated vertically. 
Position and Locality.—Rare in the carboniferous limestone of Armagh. 
Explanation of Figures.—P1. 3. I. fig. 4, front view of average tooth, natural size, with the large bony 
roots slightly imperfect at base. 
PETALODUS RECTUS (Ag.) name only. 
Ref.—Portk. Geol. Rep. t. 4. f. 9, (the vertically-striated elevated part of this figure represents a portion of the 
matrix, and not the crown of the tooth). 
Desc.—Tooth very broad, greatly flattened, crown thin, rectilinear, or nearly so; in some specimens slightly 
undulated, and marked with vertical strize near the edge in others; crown surrounded by a broad band of four 
or five imbricating lamella of ganoine; root deeper than the crown and coronal folds together ; concave in its 
upper half, tumid and longitudinally rugged below; average length of rather small specimen one inch ; height 
of crown about one line; width of coronal bands three-fourths of a line; depth of root two and a half lines. 
The great width and slight elevation of the knife-like crown of this species easily distinguish it from 
any others. The name C. rectus of Agassiz’ published lists applies to the perfect, nearly straight-edged speci- 
mens, while his name, P. marginalis, applies to the slightly worn examples, in which the edge is striated and 
undulated, and I have traced the perfect passage of one form to the other. 
Position and Locality Not uncommon in the dark carboniferous limestone of Lowick, Northumberland; 
very rare in the lower carboniferous limestone of Armagh. 
PETALODUS SAGITTATUS (Ag. name only). PI. 3. I. fig. 2, 3. 
Desce.—Crown acutely angular above, pointed in the middle, with straight sides in old individuals, but 
obscurely tricuspid in worn ones; ends arching considerably downwards; surface moderately convex and 
smooth, except when worn, which gives a coarse, fibrous, vertical striation to the margin; middle portion of 
the coronal ridges one-fourth the width of the tooth, and very prominent, the two or three bands of ganoine 
extending sigmoidally upwards from it on each side, and then arching abruptly downwards to the lateral angles 
of the crown ; posterior side concave, with the coronal bands broadly arched, and twice as far from the cutting 
edge as the front ones are; root extremely long, narrow, and prominent in the middle, sloped along the sides. 
Length of crown on the outer side averaging five lines, width six lines, length of root commonly double that of 
the crown. 
This species is most nearly allied to the P. psitéacinus, from which however it is easily distinguished by 
the broad spear-like form of the crown, produced by the greater flatness of the tooth, and the curious, narrow, 
