Day—On Acrodus. 61 
The dorsal spines which, by means of the teeth associated 
with them, we can assign to this species are in the British 
Museum,* and were formerly in my collection. Having per- 
sonally taken part in the extraction of these remains, I can 
speak confidently of the authenticity of their association; and 
as they were not mixed up with Saurian remains, or those of 
any other species of Hybodus, &c., there is no reason to sup- 
pose that their juxtaposition was in any way accidental, as some 
such groupings undoubtedly are.t 
In order to show conclusively the existence of teeth in this 
collection similar to those in the palate described, I have 
figured (Pl. IV.) four teeth which, perhaps not more so than 
the others, are easily referable to certain positions upon a 
similar jaw. Thus fig. 1 corresponds with those of our eighth 
row, fig. 2 with our seventh, fig. 3 with our sixth, whilst fig. 4 is 
a larger specimen of the curious teeth already mentioned as 
occurring in one of our fourth rows; fig. 5 is a still more re- 
markable variation from the general type. 
The spines which accompany these teeth are the anterior 
and posterior dorsal, easily distinguishable from each other by 
good characters. The anterior (Pl. IV. fig. 6) is 173 inches in 
length, but the poimt had been broken off before it was 
embedded, so that it was probably from one to two inches 
longer when perfect; the part not inserted into the body of the 
fish measures along the anterior line 134 inches, leaving 41 
inches for the inserted base. On comparing this spine with an 
anterior spine of similar dimensions (also now in the British 
Museum and formerly in my collection), and which is one of 
those usually confounded, by reason of the figures given by 
Agassiz, with Hybodus reticulatus, but which in reality belongs 
either to H. Delabechei, Charlesw., or to Hl. medius, Ag., we are 
struck with the resemblance that they have to each other. 
They are similarly proportioned and curved, and the ridges 
upon the sides and anterior face are very similar in depth and 
* I take the opportunity of acknowledging the courtesy of G. R. Waterhouse, 
Esq., and of Dr. Gunther, of the British Museum, as also of Professor Huxley, of 
the Museum of Practical Geology, in affording me every facility for the examina- 
tion of specimens under their care, and in drawing my attention to several which 
were of much interest, as elucidating my subject, aud which otherwise I might not 
have noticed. 
+ In Lord Enniskillen’s magnificent collection, at Florence Court, there is a 
portion of a Saurian containing between the ribs two spines and many large teeth 
of Acrodus nobilis; and in the Museum of Practical Geology there is a smaller 
fragment of a Saurian ‘interior’ which displays teeth, two cephalic spines, and 
part of a dorsal, of Hybodus reticulatus, associated with teeth and part of a dorsal 
spine of Acrodus latus (?). These specimens are very suggestive of the destructive 
capabilities of the Ichthyosauri. 
