Report of the State Geologist. 83 



apertural pits. In some conditions of weathering it somewhat 

 resembles Stictipora perarcta of the Upper Helderberg group 

 but may be distinguished by its more robust form, larger cell 

 apertures, and interapertural pits; from any other species, at 

 present known, from the Lower and Upper Helderberg and 

 Hamilton groups, it may be distinguished by its slender form, 

 distant bifurcations, parallel margins and interapertural pits. 



Formation and locality. — Hamilton group. West Williams, 

 Ontario, Canada. 



Prismopora dilatata. 



Prismopora dilatata, Hall. Trans. Albany Institute, vol. x, p. 193, 1881. 



Report of State Geologist for 1883, p. 50, 1884. 

 *' " ** Palaeontology of New York, vol. vi, p. 265, 



pi. Ixii, figs. 13, J 4, 1885'. 



This species is of rare occurrence. It differs from other forms of 

 Frismopora at present known in having lateral branches. It may 

 be distinguished frdm P. triquetra imd F. subconcava of the Upper 

 Helderberg group, by its much wider branches and larger, more 

 irregularly disposed cell apertures; from P. paucirama it may be 

 distinguished by the greater concavity of the sides of the branches, 

 more frequent branching, and much larger cell apertures ; from 

 F. spdrsipora by the much larger, circular and crowded cell aper- 

 tures ; from other species at present known it is distinguished by 

 its large size and frequent branching. 



Formation and locality. — Hamilton group, near Leonardsville, 

 Madison county, N. Y. 



Prismopora lata. 



Prismopora lata, Hall. Palaeontology of New York, vol. vi, p. 266. 



Not figured, 1887. 



*** * * * * ** 



This species in size approaches most nearly to P. dilatata, but 



it may be distinguished by the much less frequent bifurcations, 



the much less concave sides ; the more distant cell apertures, 



their trilobate form, and their disposition in oblique ascending 



rows ; from P. pauciramus of the Upper Helderberg group, by its 



broader form, the triangular spaces along the margin destitute of 



