434 Forty-second Report on the State Museum. 



(Tentaculite limestone) as do Styliolina and the same genus in the 

 Devonian. 



Cephaxopoda. The representation of this group is very meager and 

 a contrast to the other elements of the fauna. The genera represented 

 are Orthoceras, Oncoceras and Cyrtoceras. Of the first, the species are 

 both smooth and annulated, but can not be said to present distinctive 

 diagnostic features. Oncoceras is a Silurian genus and is of extremely 

 rare occurrence in the Lower Helderberg. The little-known species 

 of Cyrtoceras are not diagnostic. 



Crinoidea. These show, as a whole, strong Silurian affinities, seen in 

 the great abundance of Cystidians of various genera, and of species 

 of Homocrinus. The genera Mariacrinus and Edriocrinus have repre- 

 sentatives in the Devonian (Oriskany Upper Helderberg), but none 

 in Silurian faunas. It is important to observe that the Crinoids are 

 of rare occurrence in the typical exposures of the formation, most of 

 the genera and species being known from the western extension of the 

 rocks in central New York, where the thickness of the beds has con- 

 siderably diminished and the underlying Waterlimestone is well 

 developed. The majority of the species are from the lower beds of 

 the group. The Cystidians (Anomalocystites) and Homocrinus are rep- 

 resented in the Oriskany, the latter also by several species in the 

 Hamilton. 



Bryozoa. The predominant features of this group are the con- 

 siderable development of Fistulipora, Lichenalia, Polypora and Ptilo- 

 pora, expressing an emphatic harmony with the Bryozoan elements 

 of the Upper Helderberg and Hamilton; while Diamesopora, Callopora, 

 Rhinodictya may indicate Silurian affinities. 



CoralSc The individual abundance of the explanate Favositidse is in 

 accordance with the great development of reef-corals in the Upper 

 Helderberg and Hamilton. Aulopora (four species) and Striatopora 

 both attain their culmination in the Devonian. Michehnia, a genus 

 abundant in the Upper Helderberg and Hamilton, here makes its 

 first appearance. Cyathophylloids are exceedingly rare in species 

 though Zaphrentis Roemeri is very abundant in individuals. 



The Absence of Types. 

 Negative Elements. 



Among the Crustacea, the Silurian genera Ampyx, Illaenus, Asaphus, 

 Galymene, Staurocephalus, Encrinurus, Bathyurus, Sphoerexochus are 

 absent. The Devonian subgenus Gryphaeus, which, in Continental 

 faunas, ranges from the base to the middle of the Devonian, is wanting. 



