388 On the Fossil Fishes of the Carboniferous Limestone Serres of Great Britain. 
appearance the spread out diagram of the dental armature of Cestracion would 
present, as obtained by stripping off the teeth and spreading them upon a flat 
surface. Hence in attempting the restoration (‘ Paleont. Illinois,’ Vol. VI, 
p- 312, pl. viil., fig. 22), it is obvious that sufficient allowance may not have been 
made for the inrollment of the anterior portion of the jaw, thus producing an out- 
line more obtusely angular in front than may have obtained in reality. Yet, com- 
pared with the modern Cestracion, the jaws of the remarkable fish under considera- 
tion were doubtless less acutely produced forward, and, in this particular, holding a 
mean between its modern representative and some of the Rays (e.g. Trygon) in the 
relative obtuseness of the anterior extremity of the jaws. But the resemblance 
here ceases. In all other respects, as the form of the individual teeth and their 
arrangement upon the jaws, we observe unmistakable Hybodont affinities.” The 
teeth are disposed in serial rows having a convoluted inrollment from the inner 
to the outer border, aud gradually increasing in size from the posterior extremity 
to the row of large median teeth, anterior to which the rows are regularly 
diminished in size towards the symphysis. In addition to the teeth, masses of 
cartilage are preserved and certain peculiar little bodies of irregular form, but 
generally more or less circular and delicately sculptured with irregular carinz 
radiating from the apex towards the marginal borders, concave below. These are 
considered to have constituted the dermal or shagreen covering of the fish. No 
spines have been found. 
The teeth of Agassizodus present the closest affinities to those of the genus 
Orodus, Agass., they are distinguished by the prevailing prominence of the 
buttressed condition of the anterior coronal borders and the relative uniformity or 
evenness of the posterior face, besides the relatively fewer rows of accuminate teeth, 
as inferred from this feature being so prevalent in all collections of Orodi, while 
the linear forms are least commonly met with. The genus appears to be confined 
to the Upper Carboniferous or Coal Measure period, and it is not at allimprobable , 
that this genus constitutes the representative of Orodus in these horizons, since 
only a single form of the latter genus has been noticed from the Coal Measures and 
that may prove to belong to the genus Agassizodus. 
For comparison with the fossil forms, it may be well to cite the description of the 
dentition of Cestracion given by Prof. Owen (‘ Odontography,” p. 51). He says : 
“ The teeth at the anterior part of the jaws are smallest ; they present a transverse, 
sub-compressed, conical figure, with the apex produced into a sharp point ; these 
points are worn away from the used teeth at the anterior and outer parts of the 
jaw ; but are strongly marked in those which still le below the margin. There 
are six subvertical rows of these small cuspidate teeth on each side of the jaw, 
together with a median row close to the symphyseal line ; and from twelve to 
fourteen teeth in a row. Behind the cuspidate teeth, the five consecutive rows of 
teeth progressively increase in all their dimensions, but principally in their antero- 
