60 Day— On Acrodus. 
out that, apart from the rest of the specimen, I should certainly 
have regarded these teeth as belonging to a small individual of 
Hybodus Delabechei, Charlesworth. * 
Agassiz, however, has figured an incomplete series of similar 
teeth under the name of Acrodus Anningie ;¢ but, though his 
representation is sufficiently clear to enable us to recognize the 
specific identity of the two specimens, the markings of the 
teeth are not shown well enough to render any exact com- 
parison of their characters in the various rows possible. One 
remarkable discrepancy between his figure and mine is obsery- 
able, namely, that in the series figured by Agassiz there are 
portions of as many rows of teeth upon a fragment as there are 
upon the entire of one side of my specimen. It may perhaps 
be that the two specimens belonged, the one to an upper and 
the other to a lower jaw, and that the number, arrangement, 
and size of the teeth differed upon the two, as I find they do in 
the recent Cestracions. In the Museum of Practical Geology 
there is a specimen that agrees very well with Agassiz’s figure, 
and amongst the teeth there are many that are unmistakably 
similar to those now figured; the differences that are apparent 
may, in addition to the reason given above, be likewise partly 
due to the larger size of the individual to which they belonged. 
I am the more inclined to believe in considerable variations in 
the teeth of individuals from seeing in the specimen before us 
that the teeth of one jaw varied, without regularity in size and 
appearance, not merely according to position upon the same 
side, but even in the same relative position upon opposite sides. 
We may observe this especially in the fourth rows, in which the 
teeth on the right hand are considerably larger and longer than 
those on the left. In the right-hand teeth there are indications 
of five elevations, of which the most prominent is not the 
median, but the most anterior; hence these teeth have a pecu- 
liar aspect not observable in those of the corresponding row. 
Regarded as a whole, this palate indicates that the mouth of 
this species was of an expanded form, exhibiting but the 
slightest tendency towards that contraction of the anterior 
portion, which is so characteristic of the jaws of the recent 
Cestracion. 
* T believe this species to be identical with HZ. pyraméidalis of Agassiz. 
Tt Some of the teeth answer likewise to his figure of A. gibberulus. Agassiz 
appears to have been acquainted with the latter teeth before he named the fragment 
of A. Anningie, which I cannot find that he has anywhere described. As the two 
species are, however, figured side by side, and were consequently, I presume, pub- 
lished together, I feel justified in taking my choice of the two names; and I prefer 
A, Anningi@, as belonging to the best characterized specimen, and as preserving 
the name of one to whom Palzontologists are deeply indebted. 
