EASTMAN: CAKBONIFEKOUS FISHES FROM THE CENTRAL WEST. 199 



1883. De/todopsis ? convolntus St. Jolin and Wortlien, Pal. Illinois, Vol. VII., p. 1G5, 



PI. XI., Figs. 11, 12. 

 1883. Cochliodus costatus (pars) St. John and Worthen, Ibid , p. 167. 

 1897. Dehodus spatulatus J. S. Newberry, Trans. N. Y. Acad. Sci., Vol. XVI., p. 



299, PI. XXIV., Figs. 8-11. 



Thi.s .species was originally described from the Burlington limestone of 

 Quincv, Illinoi.-i, 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 tlu; 

 Burliufton 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 subseiiuent 

 formations. 



Of the posterior dental plate.s, 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 

 inroUed teeth described by St. John and "Worthen under the name o{ Deltodopsis? 

 conuoliUus, and by Newberry and Worthen as the " second" tooth of Cochliodus 

 costatus, fulfil all theoretical requirements for the anterior dental plate of D. 

 sjMtidatus, 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 Cochliodus 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 B. 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 



