ILLINOIS STATE GEOLOGICAL SURVEY 



Discussion. — Megaspores typical of Tri- 

 letes subpilosus are smaller, have shorter 

 spines and a thinner spore coat than those 

 of T. subpilosus forma major. The spines 

 may be rather widely spaced, even around 

 the contact areas and somewhat short and 

 blunt ended (pi. 2, fig. 1) . The apical ex- 

 pansion is of the same configuration as in 

 T. subpilosus forma major but somewhat 

 lower. In contrast, spores of T. horridus 

 have unornamented, expanded, flaplike lips 

 and possess distal subsidiary spines. 



The spores of Triletes subpilosus, includ- 

 ing variants, exhibit a wide range in over- 

 all diameter and spine length, both gener- 

 ally decreasing from older to younger strata. 

 The measured specimens, here referred to 

 as spores typical of the species and de- 

 scribed above, are from three coals in the 

 Caseyville Group. Those from the Battery 

 Rock Coal range from 650 to 1030 fx in 

 equatorial diameter (mean 898 [x for 8 

 spores) and possess spines from 56 to 128 yu, 

 in maximum length. Those from an older 

 coal (maceration 795) range from 555 to 

 1110 fi in equatorial diameter (mean 883 t i 

 for 10 spores) and possess spines from 66 to 

 123 /x in maximum length. Spine length is 

 generally less than 100 t x. These two assem- 

 blages are very similar, but their mean di- 

 ameters are somewhat greater than that 

 originally cited by Dijkstra (1946, p. 46) 

 for T. subpilosus. 



It is possible that the spores of Triletes 

 subpilosus are more closely comparable 

 with those of T. subpilosus forma major, 

 originally defined by Dijkstra (1952a, p. 

 103) as ranging from 500 to 1300 ^t (mean 

 866 ix for 50 spores) in total axial length. 

 Also included here as typical of T. sub- 

 pilosus are seven rather large spores from 

 the oldest coal from a diamond drill core in 

 Wabash County, Illinois (maceration 798), 

 in the Caseyville Group. These have an un- 

 usually narrow range in equatorial diam- 

 eter, 1010 to 1270 ^ (mean 1142 /x), and pos- 

 sess spines from 56 to 103 /x in maximum 

 length. Such a narrow size range is not 

 normal; the discovery of a few smaller ex- 

 amples, in addition to the few large ones 



that were found, would lower the mean con- 

 siderably. Although the mean diameter of 

 these few spores is at least 100 ^ greater than 

 that of spores of T. subpilosus forma major 

 from two older formations (Chester, mace- 

 rations 143, 166), the latter have, with a sin- 

 gle exception, longer spines. 



Spores of Triletes subpilosus are present 

 in the youngest coal of the Black Creek 

 Group and are abundant in the overlying 

 coals of the Mary Lee Group in the Warrior 

 Basin, Alabama. They also are known from 

 the Indiana French Lick Coal (maceration 

 151) and from the shale (maceration 163) 

 above the Pinnick Coal of Indiana. 



Previously Reported Occurrences. — 

 Spores typical of the species occur in Upper 

 Westphalian A and Westphalian B in the 

 Netherlands (Dijkstra, 1946) , and in Upper 

 Westphalian B to Middle Westphalian C in 

 the Ruhr Basin (Potonie and Kremp, 

 1955). 



Occurrence. — Megaspores of Triletes sub- 

 pilosus are abundant and dominant in the 

 Battery Rock Coal (maceration 587) and in 

 a coal (maceration 795) of the Caseyville 

 Group. They are common in an unnamed 

 coal (maceration 797) and are rare in the 

 "Makanda" Coal (maceration 142) and 

 lowest unnamed coal in a diamond drill 

 core from Wabash County (maceration 

 798), all of the Caseyville Group in Illinois. 



Triletes subpilosus forma major 

 (Dijkstra) ex Chaloner, 1954 



Plate I, figures 1-9 



1950 Triletes subpilosus forma major Dijkstra, p. 



871 (nom. nud.). 

 1952 Triletes subpilosus (Ibrahim) forma major 



Dijkstra (1952a), p. 103 (nom. nud.). 

 1954 Triletes subpilosus forma major Dijkstra, in 



Chaloner (1954b), p. 27; pi. I, fig. 4 (not 



pi. I, figs. 5, 6). 



Description. — Megaspores of medium size, 

 more or less bottle-shaped with distinct 

 apical prominence, usually compressed 

 obliquely; maximum equatorial diameter, 

 measured perpendicular to spore axis, from 

 465 to 1790 ^ (mean 1195 ^ for 74 speci- 



