HN 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 L. formosus. It need only be 
remarked here that the additional material proves conclusively that the spines 
of Erismacanthus occurred as rights and lefts, and are presumably referable 
to the head-region. 
The occurrence of EZ. maccoyanus in other formations than the St. Louis lime- 
stone has not been previously reported. A small branched spine, however, 
from the Kinderhook limestone of Le Grand, Iowa, belonging to the Museum 
of Comparative Zodlogy, 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. 
Hrismacanthus formosus EAstTMAN. 
(Text-figure 13.) 
1875. Erismacanthus maccoyanus (errore) St. John and Worthen, Pal. Illinois, Vol. 
VI, p. 461, Pl. XXIL,; Fig. 3. 
1902. Hrismacanthus 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 }. 
which it accompanies in the same formation, and twice the size of HE. jonesi 
M’Coy, the largest European species. It is also interesting in having paralleled 
