470 PALAEONTOLOGY OF ILLINOIS. 



CREPIPORA SIMULANS Ulrich. 



PL XXXIX, Fig. 4-4a, and PI. XL, Fig. 3-3a. 



Zoarium encrusting, sometimes forming crusts of greater or 

 less thickness, at other times irregular masses by the develop- 

 ment of successive layers. Thickness of layers varying from one 

 to five mm. Surface exhibiting at intervals of three or four mm. 

 small clusters of mesopores, which are usually abruptly elevated 

 and surrounded by zooecia with larger orifices than ordinary. 

 Apertures arranged in more or less regular curving series, a 

 somewhat concentric arrangement about the maculae prevailing; 

 rhomboidal or subpolygonal in outline, 0.22 to 0.4 mm. in 

 diameter, the average being 0.25 mm.; about seven of those in 

 the intermacular spaces in two mm. Lunarium only observable 

 at the surface of the well preserved examples. Zooecial tubes 

 scarcely prostrate at their origin, then proceeding almost direct 

 to the surface; walls thin throughout. In sections the zooecia 

 are seen to be angular, sub-rhomboidal and in contact with one 

 another; the lunarium small, with the ends projecting a little 

 jnto the zooecial cavity and composed of much lighter tissue 

 than the rest of the wall. Mesopores developed only in the 

 mature portion of the zoarium, restricted to clusters in which 

 they number from ten to forty, thick walled, rather variable in 

 size and shape, oftenest oval. Among them the observer may 

 detect very small acanthopore-like structures. Diaphragms thin, 

 about a tube diameter or more apart. 



This fine species is related to (J. venusta, Ulr., but that species 

 is essentially free and grows into irregular hollow branches. 

 The zooecial walls are also considerably thicker. In C. impressa 

 Ulr., the lunarium is much more pronounced, and the maculae 

 larger and depressed instead of elevated. 



Position and locality: Not uncommon near the tops of the 

 hills about Cincinnati, 0. I have also collected the species at 

 Madison, Ind., and seen one specimen from Wilmington, 111. 



"Jour. Gin. Soc. Nat. Hist., vol. 1. p. 93, 1878. 



