444 PALAEONTOLOGY OF ILLINOIS. 



apart, and, as usual, perforated subcentrally. Mesopores very 

 few or wanting. Acanthopores not very large, numerous, almost 

 all the angles being occupied. 



The far more robust habit of growth, larger number of a.can- 

 thopores, and somewhat thicker walls, are peculiarities which 

 , easily distinguish this species from S. ramosa,. In other re- 

 spects they are practically identical, and I do not doubt that 

 they have been developed from a common type. 



Position and locality: Chester group, Chester, 111. 



STENOPORA RUDIS Ulrich. 



PI. LXXII, Fig. 8-8b. 



Zoarium consisting of hollow irregular branches, varying 

 in size and composed of one or several superimposed layers, 

 each 1.5 mm. or less in thickness. Surface smooth, but with 

 well marked, scarcely elevated, clusters of cells, about one-half 

 larger than the average size. Apertures polygonal, those 

 of the average size 0.3 mm. in diameter, and eight in 3 

 mm. Zooecial tubes oblique and thin walled at first, then making 

 an abrupt bend, proceed directly to the surface, the walls at 

 the same time becoming much thicker. One to three bead-like 

 swellings succeed the first. Two to five perforated diaphragms 

 intersect the tubes of each layer, the first occurring at the 

 point where the tubes bend outward. Rather small acanthopores 

 occupy less than half of the angles of junction between the 

 zocecia. Divisional line between the walls of adjoining zocecia 

 well marked. 



This species makes a close approach to Anisotrypa, but the 

 acanthopores ally it rather more closely with Stenopora. Sec- 

 tions have a general resemblance to those of S. polymorpha 

 Prout, but the zocecia are larger and the acanthopores less 

 numerous. The hollow branches and large cells distinguish it 

 from the Keokuk species of the genus. 



Position and locality: Chester group. Sloan's Valley, Pulaski 

 Co., Ky. 



