Fossils of the Utica Slate. 



33 



slightly backward. This ornamentation is of an embryonic charac- 

 ter as is shown by its greater proportional development in the 

 younger stages of growth. In the first degree its base occupies one- 

 third of the entire surface of the occipital segment. Triarthrus 

 spinosus, Billings, has but two spines, one on the occipital segment, 

 and one on the eighth segment of the thorax. Both are long and curved 

 backward, the one on the thorax resembling the spine on the thorax 

 of some species in the genus Ctphaspis. 



The above closes our observations on the metamorphoses of Triar- 

 thrus Becki. Taken with Mr. Ford's discovery of the earlier meta- 

 morphoses of Olenellus {Elliptocephalus) asaphoides^^ we have 

 illustrations from American strata of the first and third order of 

 Barrande. If collectors will pay attention to the very small speci- 

 mens of trilobites, there is little doubt, but that other genera and 

 species will be added to the list. We have Asaphus platycephalusf 

 showing three segments in the thorax, and Illcenus Milleri, Billings, 

 with ten, the usual number being nine.'-^ 



Acknowledgment. To ]Mr. C. B. Dyer, and Mr. S. A. Miller, of 

 Cincinnati, Ohio, Mr. E. Hurlburt of Utica, and Rev. Wm. N. Cleve- 

 land, of Holland Patent, N. Y., I am indebted for the loan of 

 specimens. It was due to the efforts of Mr. William P. Rust, of 

 Trenton Falls, N. Y., that the large collection of trilobites was 

 obtained and also the rare graptolites and algte. 



To Prof. James Hall, I am indebted both for access to the New 

 York State Museum collections and to his private library for works 

 of reference. 



* Amer. Jour. Science and Arts, vol. xiii. 1877. 

 » Can. Nat. and Oeol. 1859. 



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