384 PALEONTOLOGY OF ILLINOIS. 



Zooecia with sub-circular apertures and a faint peristome; pos- 

 terior margin slightly more elevated than the anterior, with a 

 strong bidenticulate process (lunarium), extending nearly half 

 across the aperture, forming a ridge on the inner side of the 

 zooecia. The ridge is channelled along its inner termination. 

 A variable number of small accessory cells, with elevated sub- 

 circular apertures, is present, also a few large tumid cells 

 (ovicells?) occur among the ordinary zocecia. 



Type: Fistulipora lunatu Rominger (B. dent at a Ulrich.) 

 Range, Devonian. 



SELENOPORA Hall, Favicella Hall. Zoaria laminar or incrust- 

 ing. Inter-zooecial spaces occupied by two series of small vesicles, 

 separated by strongly elevated walls, forming the borders of 

 hexagonal concave spaces at whose centers the sub-circular 

 zooecia apertures are situated. The latter are surrounded by a 

 thin peristome, but the lunarium is obsolete. 



Type: L. circincta Hall. Range, Upper Helderberg and Ham- 

 ilton. 



? BOTRYLLOPORA Nicholson. Zoaria simple or compound; when 

 simple, consisting of small circular parasitic disks, the upper 

 surface slightly convex, and marked by numerous radiating 

 ridges which terminate before reaching the depressed center. 

 Each ridge carries two rows of small contiguous rather thick- 

 walled zooecia. The depressed interspaces are smooth at the 

 surface, but internally are occupied by comparatively large 

 vesicles. When the zoarium is compound, it may consist of a 

 large number of such disks and, by superimposition of layers 

 of them, may eventually form small masses. The spaces be- 

 tween the disks a,re mainly occupied by very large vesicles, 

 possibly of the nature of ooecia. Diaphragms, several times 

 their diameter apart, cross the zooecial tubes. 



Type. B. socialis Nicholson. Hamilton group. 



PINACOTRYPA n. gen. Zoarium consisting of thin contorted 

 expansions, with a wrinkled epitheca below. Zooecia with sub- 

 circular apertures, a well developed granose peristome, thin 

 walls and, so far as observed, no lunarium. Interspaces wide, 

 occupied by a single series of very large angular mesopores, 



