78 



Dr. H. A. Nicholson on two new Genera and 



are arranged in double alternating rows forming regularly 

 flexuous lines enclosing oval interspaces, exactly as in Betepora. 

 The oval interspaces, however, instead of constituting so many 

 " fenestrules," are the bases of so many pillars, which proceed 

 perpendicularly inwards, across a central space, to join with 

 an internal calcareous membrane which forms the innermost 

 lining of the funnel-shaped frond. 



It follows from the above description that the mouths of 

 the cells in Cryptopora neither open on the exterior of the 

 frond, as is commonly the case in Fenestella, nor upon the 

 interior of the frond, as is the case in the infundibuliform 

 species of Retepora. On the contrary, we have in this extra- 

 ordinary genus the unique arrangement that both the internal 



Fig. 1. 



Cryptopora mirahilis, Nich. : A, a partially decorticated specimen, natural 

 size ; B, a small portion of the same, showing the inner ends of the 

 perpendicular columns, enlarged ; C, another partially decorticated 

 specimen, springing from a strong footstalk, natural size ; D, part of 

 the internal surface of the intermediate layer, showing the mouths of 

 the cells and the hroken perpendicular columns, enlai'ged ; E, a small 

 portion of the frond, enlarged and somewhat diagrammatically repre- 

 sented ; F, transverse section of part of the frond, enlarged and also 

 slightly diagrammatized (a, the external smooth memhrane ; 6, the 

 intermediate sulcated layer ; c, the central space containing the cells 

 and traversed by the pei-pendicular columns ; d, the internal membrane). 



and the external aspects of the funnel-shaped polyzoary are 

 to all appeai-ance closed by a continuous calcareous membrane. 

 The cells are not placed upon either of the free surfaces of the 

 polyzoary, but occu]iy a central space, whicli lias its internal 

 wall formed by the innermost membrane, and its external wall 

 by an intermediate layer composed of tlie laterally coalescent 

 branches. The cells are situated upon the internal face of the 

 outer wall of this central space ; and the two walls are kept 

 apart by a system of pillars, which traverse the central space 

 perpendicularly, and correspond in position with the fenestrules 



