262 Eeport of the State Geologist. 



then existing. Certain forms also enjoyed a remarkable develop- 

 ment, notably the trilobites, in Aoidaspis and wonderful types of 

 Lie HAS and Dalmanites. 



This group of beds is of especial interest in view of its posi- 

 tion, transitional between the Silurian and Devonian ages, and its 

 possession of strong and very interesting f aunal relations with the 

 Niagara and Oriskany periods. Kecent discussions have brought 

 these faunal relations into prominence and have, to a certain 

 extent, necessitated a revision of this fauna. 



With a few exceptions the specimens upon which the following 

 observations are based all come from typical localities in the 

 Helderberg mountains of Albany county, N. Y. 



In this paper I have covered the ground only as far as the 

 Echinoderms, but have endeavored to include all species described 

 up to the present time from the Lower Helderberg strata in New 

 York. A few new species are described, and wherever the material 

 has afforded data as to unknown or questioned structures, this class 

 of facts is also added. This is especially noticeable in the case 

 of the genera Hindia and Keceptaculites. Of the structure of 

 the latter, a remarkable specimen has suggested a new stand- 

 point for the interpretation of its structure In the case of Hindia, 

 nothing is added to our present knowledge, but Eahff's views 

 have been completely corroborated in a few disputed points. 

 The work done in this review, while it includes some of the more 

 perplexing organisms among invertebrate fossils, does not, from 

 its incompleteness, warrant any conclusions as to the geologic 

 age of the Lower Helderberg fauna, but may form a starting 

 point for investigations which will definitely determine that 

 question. 



New Haven, June 1, 1894. 



