202 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Deltodus contortus (St. John and Worthen). 



(Plate 4, Figs. 37, 43.) 



1883. Taeniodus contortus St. John and Wortlien {ex L. G. de Koninck MS.), Pal. 

 Illinois, Vol. VII, p. 76. 



Type. — Posterior dental plate ; Museum of Comparative Zoology. 



The genus Taeniodus, with the type species of T. contortus, was held by its 

 founders to be closely related to Psephodus, from which it was stated to be 

 chiefly distinguished " by the pronounced ditferentiation of the coronal con- 

 tour." Three species from the Mississippian series, besides the type, which is 

 from the Lower Carboniferous of Belgium, were included under this genus by 

 the original authors, but are distributed by A. S. Woodward in his Catalogue 

 of Fossil Fishes between the genera Psephodus and Deltodus. We must ex- 

 press our complete concurrence with Dr. Woodward's views, and in order that 

 others may judge of what the type species of Taeniodus is like, we here figure 

 it for the first time, and would call attention to the close resemblance between 

 it and the species of Deltodus illustrated in Plates IX. and X. of the seventh 

 volume of the Illinois Palaeontology. These forms are interesting in that they 

 show very distinctly the outlines of the individual teeth of which the large 

 principal dental plates are composed. 



Formation and Locality. — Lower Carboniferous limestone ; Vise, Belgium. 



POECILODUS MCoY. 



This genus is peculiar in having the two posterior series of teeth in each 

 jaw fused into a single much enrolled plate, the coronal surface of which 

 is marked by more or less distinct transverse ridges and furrows. St. John 

 and Worthen supposed that plates of this character pertained solely to the 

 upper jaw, and regarded the triangular plates commonly referred to the genus 

 Deltoptychius as constituting the lower dentition of Poecilodus. This idea, 

 however, is not shared by any subsequent writers, and there is abundant evi- 

 dence to show that the dentition of each jaw of Poecilodus was transversely 

 ribbed. Accordingly, the species described by St. John and Worthen as 

 " Poecilodus springeri " and P. wortheni, in the seventh volume of the Illinois 

 Palaeontology, are properly transferred to the genua Deltoptychius of Agassiz. 



Poecilodus rugOSUS Newberry and Worthen. 



1866. Poecilodus rufjosus Newberry and Worthen, Pal. lUiuois, Vol. II., p. 94, 



PL VIII., Fig. 13. 

 1866. Poecilodus ornatus Newberry and Worthen, Ibid., p. 96, PI. VIII., Fig. 14. 

 1883. Chitonodus rugosus St. John and Worthen, Op. cit., Vol. VII., p. 112, 119. 



The specimens at the command of Newberry and Worthen at the time of 

 their original description of this species were very fragmentary, and more per- 



