58 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
mations to typical rays as Tamiobatis, Archzobatis, Psammodus, Janassa, 
etc., are genetically related to the Batoidei, as commonly recognized, may 
perhaps be questioned, and indeed is even denied by Dr. O. P. Hay,} 
since we should expect to find greater differences than obtain between 
modern sharks and rays, had their divergence taken place at an ex- 
tremely remote period. ‘There is no difficulty in supposing the dentition, 
general configuration of the body, and most minor characters of rays to 
have been paralleled in the Paleozoic by adaptation to similar conditions, 
such as bottom-living, amongst specialized groups which later became 
extinct ; and we are obliged to affirm that at present there is no evi- 
dence to show that the essential feature of rays, namely the attachment 
of fin-supports to the side of the head, was originated until well along in 
the Mesozoic. 
But with respect to Campodus, we may dismiss the question of its sup- 
posed affinities to rays on the ground that all available evidence points 
to a close relationship to Cestracion, the arrangement of teeth being 
essentially similar, and the mouth-cleft long and narrow, instead of wide 
and transverse. The two rami of either jaw probably included about the 
same angle between them as in Cestracion. Orodus and related Palzo- 
zoic genera undoubtedly possessed a Campodus-like dentition; and while © 
these, together with more specialized forms such as Edestus, etc., failed 
to survive the Palozoic, the primitive Cestraciont type manifested 
great longevity. 
The lateral series of teeth belonging to Campodus are already suffi- 
ciently well known, thus rendering further description superfluous. We 
need only remark that the orientation of detached teeth may be readily 
determined from the following characters: (1) The coronal buttresses 
are invariably directed outward, and the longitudinal ridge on the oral 
surface is slightly ectad of the middle line of the crown; (2) the antero- 
lateral and postero-lateral series increase in size on passing toward the 
middle of each ramus, where one of the series is sensibly enlarged ; (3) 
the coronal eminences are more elevated in one jaw, presumably the 
lower, than in the other; (4) interposed between the foremost of the 
antero-lateral series on either side are the mo§&st anterior, or as we shall 
hereafter term them, symphysial teeth, immediately to be described. 
Symphysial dentition. —'There are at present but two specimens known 
of the symphysial dentition, both of which are illustrated in the accom- 
panying figures, which are reproduced from photographs. That shown in 
1 Hay, O. P., The Chronological Distribution of the Elasmobranchs. Trans. 
Aimer. Phil. Soc., Vol. XX., p. 74, 1901. 
