26 



ILLINOIS STATE GEOLOGICAL SURVEY 



Triletes levis is apparently restricted to 

 coals of the McLeansboro Group in Illi- 

 nois. 



Triletes indianensis Chaloner, 1954 



Plate 6, figures 1-3 



1954 Triletes indianensis Chaloner (1954b), p. 28; 

 pi. II, figs. 1, 2. 



Description. — Megaspores originally 

 more or less spherical, having no preferred 

 compressional orientation, ranging from 

 820 to 1590/x in equatorial diameter (mean 

 1227 /x for 21 specimens). Apical promi- 

 nence expanded-pyramidal (pi. 6, fig. 2) , 

 sometimes slightly constricted basally, about 

 165 to 285 n in height (mean 225 p for 13 

 specimens) and 220 to 450 /x (mean 324 ^ for 

 1 8 specimens) in diameter, generally largest 

 on the largest megaspores. Trilete rays dis- 

 tinct, about 50 ti in width, up to 60 to 65 /x 

 in height (including spore coat thickness), 

 expressed as slight ridges on the bulbose 

 apical prominence. Contact areas occupy- 

 ing two-thirds to three-fourths of the proxi- 

 mal hemisphere, usually ornamented with 

 small spines less than 5 ^ in height. Arcuate 

 ridges usually not prominent, but up to 25 xx 

 in height. 



Distal spines more or less pointed to 

 blunt ended, up to 20 /x in length and basal 

 width (pi. 6, fig. 3), commonly half as large, 

 rather densely set, especially near the arcu- 

 ate ridges. Spore coat granulose, 30 to 45 /x 

 thick with extremes of 27 /x and 66 /x, 20 

 to 26 /x thick at the contact areas; deep red- 

 dish brown by transmitted light, dark 

 brown to black by reflected light. Frag- 

 ments of an inner membrane usually ad- 

 hering to inner cavity. Description as a 

 whole based on 46 specimens studied prin- 

 cipally by transmitted light. 



Discussion. — Spores from the coal in the 

 Bethel (Mooretown) Formation are prob- 

 ably identical with those originally de- 

 scribed by Chaloner (1954b, p. 28) from 

 the Beaver Bend Limestone of Indiana; 

 they have a slightly different size range, a 

 generally thicker wall, and nearly always 

 possess minute processes on the contact 

 areas. However, the distal processes of the 



two groups of spores are identical in size, 

 shape, and distribution. The coal in the 

 Bethel (Mooretown) Formation and the 

 Beaver Bend Limestone are both early 

 Chester in age. 



The apical prominence is, as Chaloner 

 stated, very thick walled and relatively 

 opaque, but the apices on many of the 

 spores from the coal in the Bethel (Moore- 

 town) Formation could be studied by trans- 

 mitted light. The three segments of the 

 prominence, probably a hyper-development 

 of the lip at the proximal pole, show a fan- 

 like grain radiating from the center of each 

 apical segment. The segments are joined 

 only along the outer edges, forming a hol- 

 low central cavity which is enclosed at its 

 base by an inner membrane (pi. 6, fig. 1). 

 Therefore, the apical prominence is identi- 

 cal in its morphology to that on spores of 

 Triletes splendidus (Zerndt) Schopf, Wil- 

 son, and Bentall as originally described by 

 Zerndt. He postulated that this upper, com- 

 pletely enclosed cavity was not a micro- 

 spore receptacle but rather served as a float 

 mechanism aiding in the dispersal of the 

 megaspores. 



The rays on the megaspores are com- 

 monly open from the arcuate ridges to the 

 base of the apical prominence, but in some 

 specimens the apical prominence is also 

 split open along the incipient suture lines. 



Spores of Triletes indianensis have a gen- 

 erally larger apical prominence than do 

 spores of T. subtilinodulatus (Nowak and 

 Zerndt) Schopf, Wilson, and Bentall. Spores 

 of both species are similar in that they re- 

 semble those of T. splendidus but are 

 smaller and bear smaller spines. 



The following species seem to be related 

 in that the spores have similar shapes, stout 

 apical prominences, and comparably shaped 

 distal processes: Triletes indianensis (early 

 Chester) ; T. subtilinodulatus (Dinantian, 

 precise age unknown); and T. splendidus 

 (late Chester, Dinantian, Namurian A). 

 Similar megaspores also occur in rocks of 

 Kinderhook and earliest Osage age in Ohio. 



Because these megaspores are most close- 

 ly comparable with those of Triletes sub- 

 tilinodulatus and T. splendidus, which Po- 



