212 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



denticles gradually merge into the widely spaced and finally obtuse tubercles 

 occurring near the base of the spine, as shown in fig. 1 a, and fig. 4 a." 



Specimens that have come to light since the time of St. John and Worthen 

 lead to the conclusion that the original of their Plate XXII., Fig. 3, which is 

 peculiar in having " approximated denticles " along the posterior spine, is the 

 young of a gigantic species recently described as E. formosus. It need only be 

 remarked here that the additional material proves conclusivelj' that the spines 

 of Erismacanthus occurred as rights and lefts, and are presumably referable 

 to the head-region. 



The occurrence of E. maccoyanus in other formations than the St. Louis lime- 

 stone has not been previously reported. A small branched s[)ine, however, 

 from the Kinderhook limestone of Le Grand, Iowa, belonging to the Museum 

 of Comparative Zoology, appears referable to this species, notwithstanding its 

 weathered condition. At all events, it agrees with the latter in size and 

 form, but we are unfortunately left in doubt with regard to the superficial 

 ornamentation. 



Formation and Locality. — Kinderhook Limestone ; Iowa. St. Louis Lime- 

 stone ; Missouri. 



Erismacanthus formosus Eastman. 



(Text-figure 13.) 



1875. Erismacanthus maccoyanus (errore) St. John and Wortlien, Pal. Illinois, Vol. 



VI., p. 461, PI. XXIL, Fig. 3. 

 1002. Erismacanthus formosus C. R. Eastman, Amer. Nat., Vol. XXXVI., p. 850, 



Text-fig. 1. 



This, the largest known species of Erismacanthus, is interesting on account 

 of its relatively gigantic size, being nearly seven times as large as E. maccoyanus. 



Fig. 13. 



Erismacanthus formosus Eastm. St. Louis limestone, St. Louis, Mo. Outer face of 

 cephalic spine belonging to the left side of the head, X J. 



which it accompanies in the same formation, and twice the size of E. jonesi 

 M'Coy, the largest European species. It is also interesting in having paralleled 



