28 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 326 



these structures are somewhat smaller, suggestive of Bromide forms (Loeblich, 

 1942, pi. 64, fig. 8). In addition to structural variation shown by the acanthopores, 

 the nature of the zooecial wall shows considerable variation in tangential section. 

 Although some specimens show clearly integrate walls throughout their section, 

 others may display integrate and amalgamate walls in the same section. Finally, 

 angular or subangular tubes, generally from about one-quarter to somewhat over 

 one-half the size of a typical zooecium, are interpreted as small zooecia rather 

 than mesopores. The paucity of closely tabulate tubes of small size in longitudi- 

 nal sections suggests that mesopores are rare. 



In longitudinal section, this species displays more structural stability, 

 although considerable variation in the spacing of the diaphragms in the axis is 

 observed; diaphragms are virtually lacking in the axial region of a very few zooecia. 

 The Spechts Ferry specimens differ somewhat from conspecific forms described 

 both by Ulrich (1895, p. 296) and Loeblich (1942, p. 433) who report that the maxi- 

 mum spacing between successive diaphragms in the axial region is three and four 

 zooecial diameters, respectively. Erection of a new species on this structural 

 difference is certainly not justified. Longitudinal sections show under high magni- 

 fication (X210) that locally and somewhat rarely a cingulum may be developed. 

 Where a cingulum is observed, the material of these secondary deposits (Cumings 

 and Galloway, 1915, p. 361) is continuous into the diaphragms. Finally, longi- 

 tudinal sections show that the distal extremities of a few zooecia are filled with 

 a dense calcareous deposit that has largely obliterated the diaphragms. 



Text figure 3 shows the variation in number of zooecia in 2 mm, measuring 

 parallel to the length of the zoarium, and in zooecial wall thickness as observed 

 in tangential section. 



Distribution. — Localities 1, 2, 4, 5, 6, 7, 8, 10. 



Types. — Hypotypes, Illinois State Geological Survey, 12P4, 12P12, 12P25, 

 12P44, 12P46, 12P47, 12P67, 12P83, 12P89, 12P90, 12P132, 12P136, 12P139, 

 12P143, 12P149, 12P156, 12P190, 12P191, 12P195, 12P198, 12P206, 12P218. 



EXPLANATION OF PLATE 7 



Figure 1 is X4; figures 2-4 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, (12P77, 4) refers to specimen 12P77 

 obtained from collecting locality 4. Structures in photographs are not retouched. 



Figure 



1-9 Stictoporella frondifera Ulrich . 1 . Surface of zoarium showing maculae 



(12P77, 4). 2. Tangential section showing zooecial wall structure 

 (12P101, 6). 3. Longitudinal section showing zooecial wall struc- 

 ture and mesotheca near base of illustration (12P184, 8). 4. Tan- 

 gential section from same specimen as figure 2 showing cingulum- 

 like structures (12P101, 6). 5. Tangential section (12P240, 6). 

 6 . Tangential section showing prominent development of centrally 

 located dark-colored divisional line between zooecial apertures 

 (12P77, 4). 7. Tangential section from same specimen as figure 5. 

 Note variation in mesopore abundance in this specimen (12P240, 6). 

 8. Longitudinal section showing bifoliate nature of zoarium (12P184, 

 8). 9. Tangential section (12P1 84, 8). 



