FRUCTIFICATIONS FROM THE MAZON CREEK FLORA 13 



Non-soral sporangia are equally distributed on the lower laminar surface, 

 and there are 40 to 50 sporangia on a pinnule (text fig. 6A) . Sporangia are free, 

 globose, sessile, and 0.4 mm in diameter. 



The trilete spores are triangular to rounded triangular in equatorial outline. 

 The corners are well rounded and the interradial sides are straight to slightly con- 

 vex or, rarely, concave. Laesurae extend about two-thirds the length of the spore 

 radius (about 12 |am), and sutures are distinct, open, and simple. The exine is 

 unornamented in the area of the trilete marking. Ornamentation is found mostly 

 on the distal face and consists of low rugulate projections. Fifty to seventy per- 

 cent of the distal surface is covered by rugulae that are 4 to 6 \±m wide and ex- 

 tend up to 1.8 |jLm beyond the margin, which has a scalloped appearance. Some 

 specimens show development of larger rugulae near the corners. Rugulae are 

 commonly shingle-like, rising gently above the spore surface and ending abruptly 

 at its highest elevation. Twelve to fifteen arcs project beyond the margin. The 

 spore wall is about 1.5 fim thick. The diameters (46 specimens) range from 23 

 to 35 [im, with an average of 28 \±m. 



Discussion.— As sporae dispersae, the spores of Myriotheca scaberrima 

 are correlated with Camptotriletes triangularis Peppers, 1970. The spores of 

 Myriotheca scaberrima are smaller, thicker, and more coarsely ornamented than 

 those of C_, triangularis (36 to 49 |j.m in diameter). However, these discrepancies 

 may be attributed to differences in preservation, in preparation for study, or per- 

 haps in maturity. Converrucosisporites armatus (Dybova and Jachowicz) Smith 

 and Butterworth (1967) is somewhat similar but is coarser and has a verrucose 

 exine. Camptotriletes triangularis has been observed in strata between the Col- 

 chester (No. 2) Coal and Summum (No. 4) Coal, but it is rare. 



Sellards (1902), the first paleobotanist to describe spores in situ from the 

 Mazon Creek flora, discovered triangular spores having concave sides and di- 

 ameters of 36 to 40 |j.m in Myriotheca scaberrima . No remarks on the ornamenta- 

 tion of the exine were given. The spores of M. desaillyi were described without 

 illustration by Potonie (1967) from a slide preparation by Kidston. These spores, 

 which were considered immature, are subtriangular to circular and flatly verrucate. 



The present location of the holotype of Myriotheca scaberrima is unknown. 

 It was found on shale from Morris, which is in the mining area around Mazon 

 Creek. Therefore the stratum typicum probably would be equivalent to the Francis 

 Creek Shale. The specimen described by Sellards (1902) is in the collection at 

 Yale University. Sellards (1902) noted that his specimen differed from Lesquereux 1 £ 

 description in that it lacked hairs on the pinnule-bearing axis. However, Les- 

 quereux' s description referred mainly to the pinnae-bearing axis and the "verrucose 

 points" can only "indistinctly [be] seenon some part of the secondary branches 

 [pinnule-bearing axes] " (Lesquereux, 1870, p. 408). Therefore, there is no con- 

 tradiction and the determination is correct. The third specimen was figured by 

 Langford (1958) and was investigated by the authors. It is covered with a thin 

 film of white mineral matter, which obscures the spores. When covered with 

 xylene, some of the spores float off. Cell patterns of the sporangia cannot be 

 seen. The sporangia were apparently round with a very smooth surface. Two 

 other specimens are in the collection of the Field Museum, Chicago. 



Myriotheca scaberrima is similar to M. desaillyi. The only difference is 

 that the sporangia of M. scaberrima are larger. As both species are based on a 

 small number of specimens, they might prove to be conspecific when more speci- 

 mens are found. Myriotheca scaberrima and M_. desaillyi are clearly different 

 from the other species, which have larger sporangia and larger and differently or- 

 namented spores. 



