488 PALEONTOLOGY OF ILLINOIS. 



width of the monticules. Apertures irregularly arranged, the 

 interspaces being of variable width, those upon the monticules 

 more separated than the others; varying also in size and shape, 

 some being circular, others oval or sub-triangular. 0.29 to 0.30 

 mm. in diameter, and seven or eight in three mm. Lunarium 

 or hood moderately developed, occupying one side of the aper- 

 tures. Ocecia numerous, but without regularity of arrangement, 

 sometimes a number occur in close proximity to each other; 

 bowl-shaped, about three times as wide as the zooecia, with 

 prominent margins, circular or irregularly indented by the en- 

 croaching zooecia; in their perfect state, as shown by well pre- 

 served specimens, over-arched by a dome-shaped covering, 

 having a small round or crescentic opening upon one side. 

 Center of branch, in the specimens at hand, crushed out of 

 shape. Zooecia rectangular to surface in the latter part of their 

 course; provided with fairly numerous, thick, flat, or sometimes re- 

 curved diaphragms. Vesicles surrounding the zooecia in a single 

 or double series, uniform in depth, angular, variable in size and 

 shape, replaced near the surface by calcareous tissue, which is 

 perforated by numerous, small, longitudinal, irregularly arranged 

 tubuli, establishing communication between the surface and 

 vesicles. Lunarium composed of lighter colored tissue, occupy- 

 ing about one-third of the circumferance of the zocecium. 



In the form and general aspect of the zoarium this species 

 resembles Fistulipora. compressa Rominger, a common species 

 of the Keokuk limestone. Indifferently preserved examples might 

 be confounded, but when in a good, or even in the ordinary 

 state of preservation, the ocecia of the one serve excellently in 

 discriminating between them. 



Position and locality; Keokuk group, Bentonsport, Iowa, 

 and Warsaw, 111. 



STROTOPORA DERMATA Ulrich. 







PL LXXVII, Fig. 8-8a. 



This species like S. foveolata, the type of the genus, consists 

 of compressed branches, but they are much less robust in every 

 respect, the thickness being seldom more than two mm. The 

 branches too seem always to have been hollow, with an epithe- 



