48 



ments joined to form radially or bilaterally 

 symmetrical bodies, their symmetry depend- 

 ing upon the number and arrangement of the 

 segments. The microfossils are usually in good, 

 flattened compression, but many are folded. 

 Straight grooves are present on one side of 

 the body where the segments are joined, and 

 adjacent to the grooves are elevated, flattened 

 ridges or folds. These grooves and ridges are 

 absent along the smooth margin of the micro- 

 fossils. The number of segments in the speci- 

 mens observed varies from 5 to 15, usually an 

 odd number. The specimens having five seg- 

 ments are quite common and are probably the 

 basic pattern. They are boat shaped, with two 

 segments at one end, one at the opposite 

 more pointed end, and two in the middle. 

 In the largest specimens two to four seg- 

 ments in the center are usually bordered by 

 other segments. If some of the bordering 

 segments are missing, the indentations (usu- 

 ally three) thus formed have smooth margins 

 except where the segments appear to have 

 been torn out. The microfossils are seen to 

 be levigate under oil immersion objective and 

 are 1 to 2 ft thick. Dimensions (33 speci- 

 mens) : over-all size range, 50.2 to 123.2 ^ 

 in maximum diameter, median, 68.1 /x; indi- 

 vidual segments, 24.4 to 39 ju in maximum 

 diameter, median, 29 /x. 



Holotype. — Plate 8, figure 17; negative 

 5901; Trivoli Cyclothem, maceration 1175-E, 

 slide 4, coordinates, 131.8 X 41.3; size, 69.7 

 by 66.7 [i. 



Paratypes. — Plate 8, figure 18; negative 

 5688; Henshaw Formation, maceration 1122- 

 A, slide 41 ZB, coordinates, 143.6 X 41.0; 

 size, 122.5 by 101.1 /x; figure 19; negative 

 6124; Trivoli Cyclothem, maceration 1175- 

 C, slide 17, coordinates, 134.8 X 50.7; size, 

 57.7 by 48.9 /*. 



Discussion. — Although there is considerable 

 variation in the number and arrangement of 

 segments, all the specimens are placed in the 

 same species because they probably represent 

 di He rent stages of development. 



Felix (personal communication, 1963) has 

 reported that Centonites is especially promi- 

 nent in subsurface material of late Missouri- 

 an age from Harper and Beaver Counties of 

 Oklahoma and is regarded as a useful strati- 

 graphic marker for the Missourian of that 

 area. 



Derivation of name. — The species name re- 

 fers to the symmetrical arrangement of the 

 segments. 



DISTRIBUTION OF 

 SMALL SPORE GENERA 



SPORES OF THE 

 TRIVOLI CYCLOTHEM 



The Trivoli Cyclothem of the Modesto 

 Formation was first described by Wanless 

 (1931, p. 182, 192). His generalized section 

 showed the cycle delineated by a sandstone 

 at the base and a shale at the top. Wanless 

 (1957, p. 121-122, 193) later described the 

 cyclothem in detail from its type exposure 

 in Peoria County. 



For this study, spores of the Trivoli Cyclo- 

 them were examined from two Illinois dia- 

 mond drill cores, one from Macoupin County, 

 the other from Franklin County, so that as- 

 semblages of substantially the same strati- 

 graphic interval but different localities could 

 be compared. Both core sections are de- 

 scribed at the end of the report. 



Macoupin County, Illinois 



From the Macoupin County core, macer- 

 ated samples from the Trivoli Cyclothem and 

 the overlying 8 feet of strata were examined. 

 Text figure 13 shows the distribution, in per- 

 centage, of small spore genera found. Of 

 the six samples (macerations 1128-A through 

 1128-F) from strata below the No. 8 Coal 

 that were macerated, only that of the un- 

 derclay directly below the coal yielded spores, 

 and they generally were poorly preserved. 

 Although spores were obtained from macera- 

 tions of all the samples above the coal, they 

 were not abundant in relation to the amount 

 of fine organic matter. Spores in the shaly 

 limestone (maceration 1128-K) were greatly 

 eroded and specific identification was diffi- 

 cult. The least diversity of spore genera and 

 species, which can be partly attributed to 

 lack of preservation, occurred in the under- 

 clay and shaly limestone, whereas the great- 

 est diversity was found in the coal, where 

 preservation of spores was good. To conform 

 to the system of nomenclature outlined by 



