218 NEW YORK STATE MUSEUM 



they are sometimes in contact, at other times distant the diame- 

 ter of an individual or more; exterior with annulations and 

 wrinkles of growth; costae distinct; alternate septa very 

 short; sides of septa carinated as in H e 1 i o p h y 1 1 u m, 

 but their margins very seldom denticulate. Internally the 

 peripheral region is occupied by cysts, which in a longi- 

 tudinal section have the appearance of being arranged in 

 vertical rows; tabulae strong, usually horizontal, and at varying 

 distances apart. 



In the type species the corallites are straight and rigid, and I 

 have observed no lateral excrescences or expansions. 



The internal structure of this genus is essentially the same as 

 in Heliophyllum, but the manner of growth and general 

 appearance is such that it could not be included in that genus. 



In a longitudinal section the structure appears similar to that 

 of the more robust forms ofSynaptophyllum. In a trans- 

 verse section the appearance is very different. Externally it may 

 be easily distinguished from that genus by the absence of the 

 lateral processes, which are a distinguishing feature of S y n a p- 

 t ophy 1 1 u m. 



In exterior it resembles Placophyllum, but differs in in- 

 ternal structure. 



Prismatophyllum, gen. nov. 



Type: Prismatophyllum rugosum, E. and H. Monographic des 

 polypiers fossiles. 1851. p. 387, pi. 12, fig. 1, 1^, 1^, and Cyatho- 

 phylkcm rugosum, Rominger, Fossil corals. 1876. p. 166. 



Example, Acervularia davidsoni E. and ll. Monographie des 

 polypiers fossiles. 1851. 



Colonies forming masses composed of prismatic corallites, in 

 contact with each other, and of essentially the same diameter for 

 their entire length. While the internal structure of the genus 

 is very similar to that of H e 1 i o p h y 1 1 u m, the prismatic form, 

 mode of growth and reproduction are so widely different from 

 the typical forms of that genus that they should not be included 

 in the same genus. 



