NIAGARA URODP. 115 



Fig. 4 m. A small specimen, showing a section through the centre, with deep transverse cup- 

 form septa. 



Fig. 4 n. This individual shows apparently lateral budding, but the appearance is probably due 

 to the cessation of growth at the point o, where the animal had contracted the cup; 

 and from this cell originated three young polyps, the stronger growing more up- 

 rightly and pushing out the others to one side. 



Position and locality. In the lower part of the Niagara limestone, associated with the pre- 

 ceding and following species. (State Collection. Colleelion of Ci>\. JEtvii-n, ice.) 



Genus DIPLOPHYLLUM {nov. gen.). 



[Gr. 5i*Xoo?, duplex, and (puXXov, folium ; in allusion to the duplex character of the cell.] 



Simple, ramose or aggregate cylindrical stems ; corallum composed of two distinct portions, 

 the inner transversely septate, the outer with fine transverse dissepiments uniting the lamellae 

 which are continuous to the centre ; cell deeply concave in the centre, and separated from the 

 outer portion by a distinct rim ; both the inner and outer portions stellate with the same num- 

 ber of rays. 



The distinguishing features of the genus are the diflFerence in the characters of the central 

 and marginal areas of the cell, which are distinctly separated from each other, as shown in 

 longitudinal sections. 



This genus is apparently related very nearly to the Diphyphyllum of Loksdale (Geology 

 of Russia and the Ural Mountains, Appendix), preserving also more intimate relations to 

 Cyathophyllum, Columnaeia and allied genera, but requiring separations upon sufficient 

 grounds, if we are to give to the numerous forms of this family names of any definite signi- 

 fication. The generic names proposed for the species here described sufficiently indicate their 

 difference from the Cyathophyllae ; and instead of applying that generic term to all the 

 Silurian corals having any general resemblance to the genus, we have the means of giving 

 geological value to the type. 



I may remark in this place, that thus far we have not found a single species of the Genus 

 Cyathophyllum, as limited by recent authors, in any rock below the Onondaga limestone. It 

 seems, therefore, that notwithstanding the representatives of this type came into existence at 

 very early geological periods, still no species having the structure of Cyathophyllum ceratites 

 of GoLDFUss is known throughout the Silurian rocks of America, if we limit the application of 

 that term to those rocks below the Oriskany sandstone. 



The rocks of the Niagara period, from which these fossils are described, is regarded as 

 equivalent to the Dudley or Wenlock formation of England ; and although we have the family 

 Cyathophyllidea represented by Streptelasma, Caninia, and the three new genera here intro- 

 duced, we have no true Cyathophyllum ; nor have we Cystiphyllum, or Heliophyllum at 

 the same period. These are all typical of certain geological periods ; and by attending more 

 minutely to their structure, they become valuable e%-idences of the age of the rock in which 

 they occur. 



