-490 PALEONTOLOGY OF ILLINOIS. 



with the internal ridge and lunarium. Also the vesicles of the 

 interspaces. Diaphragms are few or absent in this example. 

 Hall says septa (diaphragms) are "frequent." 



Position and locality: Middle Devonian, (Upper Helderberg?), 

 Falls of the Ohio. 



BOTRYLLOPORA Nicholson, 1874. 



(Can. Jour., vol. XIV, No 2. 

 (For generic diagnosis see page 384.) 



BOTRYLLOPORA SOCIALIS Nicholson. 



PI. XLin, Fig. 9-9b. 



Botryllopora socialis Nich.,1874. Geol. Mag. n. s.,vol. I, p. 160, PL IX, fig. 16. 

 Botryllopora socialis Nich.,1874. Pal. Ont.. p. 96, fig. 32. 

 Botryllopora socialis Hall, 1884. Kept. State Geol. for 1883, p. 61. 



Zoarium rarely solitary, generally consisting of a greater or 

 less aggregation of approximate or confluent disc-like colonies, 

 attached by their lower surface to foreign bodies; rugose corals 

 and Brachiopods seeming to be the most favored. Sometimes 

 specimens are found that are free, with a strongly wrinkled 

 epitheca below. These again may consist of several successions 

 of colonies growing one upon the other. Ordinarily, however, 

 there is but one layer of about one mm. in thickness. Diameter 

 of discs varying from two to four mm. Upper surface of disc 

 convex with a central cup-shaped or flattened depression, from 

 which radiate a number of depressed linear spaces, all of about 

 the same width, commonly bifurcating about half way out. 

 Between the depressed spaces are ridges that extend nearly to 

 the margin of the disk; about half way between the center and 

 the margin their number is usually doubled by the interpola- 

 tion of shorter ridges. Total number of ridges varying from 

 fifteen to twenty-five. Each ridge is occupied by two series of 

 zocecia, having rather thick adjoining walls, there being no in- 

 terspaces between them. Zooecia apertures circular or oval, less 

 than 0.10 mm. in diameter, about eight in one mm., (the 

 length of the long ridges) with horizontal or slightly concave 

 diaphragms, about three tube diameters apart. Central and 



