4 The American GeoUxjist. January, 1895 
be counted, so tliat there is little room to doubt tliat this was 
the normal minimum number on one face, which number is of 
course much below the total. 
To the eleven files of teeth on this portion of the maxillary 
must be added two more on the separated anterior part, com- 
posed of similar teeth, raising the whole number to thirteen ; 
and, from a comparison with other specimens allied to this, I 
am induced to believe that this is the normal number and 
that it is seldom if ever exceeded, or, if exceeded, that the ex- 
cess is small. 
The teeth are all of the same general form and consist of a 
semi-elliptical base and a main cusp with one diverging den- 
ticle on each side, as shown in the enlarged figure. Occasion- 
ally there are traces of very minute additional denticles, and 
on some of the teeth the single lateral one is reduced to a very 
small size. The teeth are quite smooth on their fiat or outer 
face and but very faintly striate on the rounded or inner side. 
They fit close against one another, the lower lying in the 
slight concavity in the outer surface of the one immediately 
above it. 
It is not possible to determine from this specimen whether 
there was a median file of. teeth in the front of the maxillary; 
but no evidence is found against their existence. 
In the mandibles, which are in far less perfect condition, 
the files of teeth are less clearly traceable. Ten are visible, 
however, on the left side of the head ; and there is room be- 
side these, where fracture has destroyed the evidence, for 
about two more. There is also distinctly visible a median 
symphysial file of teeth similar to the rest, of which two ma}'^ 
be seen in the drawing. The total number, therefore, cannot 
have been very different from that in the upper jaw. 
Admitting, however, that there were no more that the num- 
ber for which the evidence is indisputable, we have the fol- 
lowing result : There were twenty-six files of teeth in the up- 
per jaws, and twenty-five in the lower, making fifty-one in all ; 
and if there were on an average only ten teeth in every file, 
there must have been more than five hundred teeth in the 
mouth of (Jladodus clarki. 
The Branchial Arches. In consequence of the crushed and 
broken condition of the cartilages behind the head, it is difii- 
