PALMOZOIC ROCKS IN CANADA AND SCOTLAND. 385 
edge thirteen, subequal, blunted, minute teeth. Length ? line, 
width 2 line. 
ARABELLITES PoLITus, Hinde. (Pl. XX. fig. 19.) 
Jaw consisting of a nearly flat plate, the front portion rounded 
and extending below obliquely to a point, the posterior extremity 
slightly truncate ; on the sloping upper edge is a series of twelve 
pointed teeth, the first of which, though not larger, is opposed in 
direction to the rest and slightly claw-shaped. Length of the 
toothed border 3 line, and from the summit to the point 4 line. 
ARABELLITES SIMILIS, Var. ARCUATUS. (PI. XX. fig. 20.) 
In the Hamilton group there are comparatively numerous spcci- 
mens which I am unable to distinguish from <A. similis from the 
Niagara formation; but in addition to these there are certain ex- 
amples which show differences which may entitle them to be sepa- 
rated as a variety from that form. In the specimen taken as a type 
of this variety the jaw is crescentiform and slightly concave, the 
upper border arched and with about fourteen small teeth, of which 
the third is larger and more upright than the others. About 3 line 
in length. 
It is amore arched form than A. similis, and has a greater number 
of denticulations. 
Genus Nererpavvs, Grinnell. 
Nereidavus, American Journal of Science, Sept. 1877, p. 229. 
This genus was proposed by the author for fossil jaws resembling 
those of the existing genus Nereis. I have only found one example 
which, in my opinion, can be placed in the genus. 
NEREIDAVUS soLITaRIus, Hinde. (Pl. XX. fig. 12.) 
Jaw compressed and relatively wide; at the truncated posterior 
end of the jaw is a small concave portion which is distinctly marked 
off from the rest of the jaw by a transverse ridge; in front is a 
prominent tooth directed forward and slightly out of plane with the 
rest of the jaw, and on the upper border are ten small, blunted, 
nearly upright, triangular teeth, followed by numerous very minute 
crenulations. Length 14 line, greatest width 2 line. 
The forward inclination of the anterior tooth and the marked off 
portion at the extremity of the jaw, which may have served for a 
muscular attachment, lead me to think that this may have been one 
of a pair of jaws carried in the front of the head like those of Nereis ; 
in all the examples of that genus, however, which I have seen, the 
smaller denticulations are directed forward towards the larger tooth, 
whereas in this fossil example they are nearly upright. As a rule, 
too, the smaller teeth in Nereis are fewer in number than in this 
example ; but this is a feature very liable to variation. 
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