WELLBURX : OX THE GENUS MEGALICHTHYS, AGASSIZ. 
65 
the rest of the surface being set with similar but smaller teeth, 
which are more distant ov^er the anterior portion of the bone, 
bub posteriorly pass into a dense rasp of minute denticles. Out- 
side these the edges of the maxillse are set with small, conical 
teeth, continuous in front with those on the edge of the pre- 
maxill^e. 
Lower dentition. — The outer edge of the dentary bone of the 
mandible bears a row of small, conical teeth. Within these are 
four large, strong, conical teeth, which are distantly placed. The 
^interior one is the largest, and is firmly socketed in the thickened 
symphisial extremity of the dentary bone, the others lie within 
the edge of the dentary bone, and are attached to the series of 
laniary bones i^\x XYIII.). The edge of the sphenial bone also 
bears numerous rasp-like teeth. 
From the above it will be seen that the dentition is that of 
a predatory fish. 
Teeth. — External characters. They are round in transverse 
section, conical, more or less curved, bases plicated, and many 
are covered with very fine stride, which merely involves the outer 
portion of the enamel (Young, Davis). These lines are some- 
times parallel or anastomose to form a fine reticulation. 
Internal characters. — The walls of the teeth are infolded, 
the folding being simple at the commencement of the external 
fluting, but as we pass towards the root the folds become wonder- 
fully beautiful and complex, but the vertical tubes formed by the 
infolding never form such an interlacing network as in the 
Dendrodont type (Dr. Traquair)."^ 
The gill flap, anteriorly and inferiorly, is completed by a 
series of bony plates, the jugulars, which lie between the mandi- 
bular rami, and which, together with the infraclavicular bones 
which lie along their posterior border, cover in and protect the 
underlying branchial arches. 
In the centre are two elongated plates, the principal jugulars 
(P.J.). They are broader behind than in front ; their posterior 
*Geo. Mag., Dec. III., Vol. VIII., No. 321, p. 123. 1891. 
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