FISHES OF THE CARBONINEROUS SYSTEM. 193 
somewhat in pronouncing the late discovery of Mr. McAdams distinct from 
the one which he formerly made in the same quarries at Alton. ‘That is, 
I have thought it possible that the jaw of Calosteus might have belonged to 
the same fish, but it will be noticed that in Calosteus the pits which mark 
the positions of the great laniary teeth are almost equally spaced and are 
closely approximated ; furthermore, in Calosteus there is no indication that 
the mandible was segmented; on the contrary, it was evidently solid through- 
out. In Rhizodus, on the other hand, the laniary teeth are irregularly spaced, 
few in number, and remote from each other; characters conspicuous in the 
jaw now described, but wanting in that to which the name Cwlosteus was 
given. 
Again we have in Celosteus no indication of the pitting and tubercula- 
tion of the external surface so conspicuous in Rhizodus, and the anterior 
extremity of the dentary bone is not tumid. Hence, with the material now 
before me, I am led to believe that the jaws obtained by Mr. McAdams 
belong to two allied but distinct fishes. 
It is probable that the discovery of these curious remains by Mr. 
McAdams will stimulate further and careful search for other traces of the 
great fishes they represent, and there is no doubt that material will be ob- 
tained sooner or later which will clear up all questions in regard to their 
structure and relations. 
The Saint Louis limestone is exposed at a great number of localities in 
Indiana, linois, and Missouri; and at Greencastle, Alton, Saint Louis, and 
other places it has yielded a large number of fish remains, and it has there- 
fore been already somewhat carefully exploited, but no trace of the great 
fishes now described, not even of any Ganoid, were obtained from it up to 
the time when Mr. McAdams discovered the jaw of Cwlosteus. We may 
therefore infer that these fishes were not numerous in the Carboniferous 
seas, and many years may elapse before we shall get a more complete 
record of their lives. 
In the splendid collections of fish remains made from the Mountain 
limestone by Professor Worthen, Mr. Van Horne, My. St. John, and others, 
so fully illustrated in the reports of the Geological Survey of Ilinois, it will 
be noticed that no traces of Ganoids appear, while the teeth and spines of 
MON XVI -13 
