92 SAUROCEPHALUS AND ITS ALLIES. 
The teeth in the corresponding bone of both species are very nearly alike in form; and 
they have the same mode of insertion and order of succession as in the existing Sphy- 
rena. The crown or exserted portion of the tooth, with a thin enameloid investment, is 
compressed conical, with trenchant borders and an acutesummit. The transverse section 
near the base is carinated at the poles, convex externally, and trilateral internally. In 
S. lanciformis the crown is straight; its breadth equal to its length, and the thickness half 
the extent of the breadth; and the trenchant borders are finely denticulate. In S. Leanus 
the crown is slightly curved inwardly; its length is a third greater than the breadth; and 
the trenchant borders are entire, and extend more upon the fang than in the former. 
The fang is from two to three times the length of the crown, and tapers towards its free 
extremity. Internally it is convex, and externally trilateral with the intermediate face 
grooved, which condition often extends upon the corresponding face of the crown as 
represented in the enlarged figure 15. 
The surface of the crown is striate, but so very minutely that the elevation of the 
strize is hardly perceptible. This condition is distinct from the more visible structural 
folding in the enameloid substance. 
In the maxilla of S. lanciformis a layer of coarsely granular ossific substance, which 
invested its outer surface, accumulates at the dental border and envelopes the base of the 
teeth, and on the inner side of the jaw is defined by a groove containing a series of 
foramina communicating with the cavities of the successional teeth. In S. Leanus a 
similar layer invests the outer face of the jaw, but does not accumulate at the dental 
border, where it ceases abruptly. In this species on the inner side of the dental border, 
vertical notches exist opposite the teeth, terminating below in foramina communicating with 
the reserved cavities for the successional teeth, as seen in fig. 13. 
tn the specimen of S. Leanus the premaxillary is a quadrate curved bone united by suture 
with the anterior border of the maxillary, and turned inward at the border where it joins 
the corresponding bone of the opposite side. Its dental border appears to have supported 
ten teeth, of which those posterior are of the same size and form as those of the maxillary 
bones, and the anterior ones, though broken away, judging from the remains of their 
alveoli, appear also to have been of the same size. The contiguous parts of the premax- 
illary and maxillary bones at their upper part support a tubercle with a smooth surface, 
as in fishes ordinarily. (Fig. 12, a, b.) 
In the shortness of the premaxillary, its union and continuity with the maxillary, and 
the support of teeth by the latter, we have an extraordinary variation from the condition 
of things as existing in the living Sphyrena; and indeed the two bones in their form, re- 
lative position, union, and continuity of the dental borders, exhibit a striking resemblance 
to the same parts in the lacertian reptiles. 
