14 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 326 



Homotrypa dickeyuillensis is related closely to H. subramosa and H. callosa 

 described by Ulrich (1895, p. 239, 240; 243, 244). H . dickeyvillensis differs 

 from H. subramosa in that the latter species has diaphragms spaced from one to 

 three zooecial diameters apart in the axial region and may have more prominent 

 and more abundant acanthopo res . In H. dickeyvillensis J however, diaphragms are 

 much more distantly spaced in the axis and display a tendency to occupy similar 

 levels or horizons in adjacent zooecia throughout the width of the axial region. 

 H. dickeyvillensis differs from H. callosa in the frequency of diaphragm occurrence 

 in the axial region and in details of zooecial wall structure as observed in tangen- 

 tial section. Ulrich (1895, pi. 20, fig. 19) illustrates a specimen (presumably 

 regarded by him as a cotype or paratype) of H. callosa that clearly has more abun- 

 dant diaphragms in the axis than has H. dickeyvillensis. In tangential sections 

 of H. dickeyvillensis, the thin black divisional line, so well developed in H. 

 callosa (Ulrich, 1895, pi. 20, figs. 15, 20) is developed very sporadically and 

 imperfectly; further, the granular wall structure (Ulrich, 1895, pi. 20, fig. 21) 

 was not observed in tangential sections of H. dickeyvillensis. 



This species is represented in the Spechts Ferry collections by one speci- 

 men from which two tangential and two longitudinal sections were prepared; a large 

 fragment of the zoarium remains. The specific name alludes to the collecting site 

 of the holotype, which is located near the village of Dickeyville in Grant County, 

 southwestern Wisconsin. 



Distribution. — Locality 5 . 



Type. — Illinois State Geological Survey; holotype 12P88. 



EXPLANATION OF PLATE 3 



Figure 5 is X4; figures 2 and 6 are X60; all others are X20. 



Specimen number and collecting locality are shown in parentheses follow- 

 ing explanation of each figure; for example, (12P162, 8) refers to specimen 12P162 

 obtained from collecting locality 8. Structures in photographs are not retouched. 



Figure 



1-6 Dekayella praenuntia echinata Ulrich. 1. Tangential section (12P162, 8). 

 2. Small area of tangential section displaying excellent examples of 

 larger set of acanthopores (12P148, 4). 3. Longitudinal section 

 (12P162, 8). 4. Tangential section showing part of monticule in upper 

 third of illustration (12P92, 6). 5. Surface of zoarium showing monti- 

 cule (12P154, 1). 6. Tangential section displaying acanthopores of 

 two distinct sizes (12P121, 4). 



7-9 Prasopora simulatrix orientalis Ulrich. 7. Tangential section showing 

 macula (12P1, 6). 8. Longitudinal section showing prominent cysti- 

 phragms and closely tabulate mesopores (12P1, 6). 9. Tangential 

 section (12P15, 4). 



