EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 199 
1883. Deltodopsis ? convolutus St. John and Worthen, Pal. Illinois, Vol. VII., p. 165, 
Plex Figs..11,, 12. 
1885. Cochliodus costatus (pars) St. John and Worthen, Jdid., p. 167. 
1897. Deltodus spatulatus J. S. Newberry, Trans. N. Y. Acad. Sci., Vol. XVL, p. 
299, Pl. XXIV., Figs. 8-11. 
This species was originally described from the Burlington limestone of 
Quincy, Illinois, and the fact that it possessed a continuous range from the 
Kinderhook to the Keokuk inclusive has not previously been made known. 
In the earliest horizon the teeth are sparse and of relatively small size; in the 
Burlington group it is perhaps the most profuse of all Deltodus teeth; and 
although moderately large forms, such as is shown in Plate 4, Fig. 41, are 
occasionally met with in the Keokuk limestone, none are found in subsequent 
formations. 
Of the posterior dental plates, the more strongly arched forms may be pro- 
visionally referred to the lower, and the less strongly arched to the upper jaw. 
The anterior dental plates belonging to this species have not been heretofore 
definitely recognized as such, no specimens having been found which show the 
two principal plates in natural association. An examination of a considerable 
amount of perfect material, however, has satisfied the writer that the strongly 
inrolled teeth described by St. John and Worthen under the name of Deltodopsis ? 
convolutus, and by Newberry and Worthen as the “ second ” tooth of Cochliodus 
costatus, fulfil all theoretical requirements for the anterior dental plate of D. 
spatulatus, and may be referred with utmost confidence to that species. The 
superficial characters of the two forms are identical, as already observed by St. 
John and Worthen, they are of corresponding proportions and curvature, and 
there is a perfect coadaptation of their grooved lateral edges, as any one may 
be convinced by fitting the two forms together in their natural position. 
According to the view here advocated, the species known as Deltodopsis ? 
convolutus St. J. and Worthen becomes synonymous with D. spatulatus ; and 
on removing from the so-called Oochliodus costatus Newb. and Worth. the 
form described by these authors as the “second” tooth, there remains as type 
of the latter species the narrow, doubly plicated form described by them as 
the “third” tooth. St. John and Worthen have expressed the opinion that 
the original authors were mistaken in regarding this as a “ third,” or posterior 
dental plate, believing it 'to represent the anterior of the two principal grinding 
plates ; but evidence is lacking for associating it with any degree of assurance 
with other described species. 
From the circumstance that the antero-lateral margin of the “second” or 
anterior dental plate in D. spatulatus is deeply grooved, as if for ligamentous 
union with a contiguous plate, Newberry and Worthen were led to infer the 
existence of a single dental element in advance of this “second” plate, thus 
postulating one more than the number of grinding organs characterizing the 
dentition of all Cochliodonts so far as known. Cochliodus latus Leidy fur- 
nishes us with perhaps the most complete example of Cochliodont dentition 
