38 



PALEOZOIC FOSSIL SPORES 



Rcuiar'ks. — This genus is reported in 

 only two instances, in the Ruhr and in 

 IlHnois, in both cases from relatively few 

 specimens. The forms have been assigned 

 to different species as listed below. Much 

 more information is needed before their 

 significance can be understood. 



1. ZONALO-SPORITES AUREOLUS (Schopf) S. W. 



and B., comb. nov. 



Monoletes aureobis Schopf, 1938, Illi- 

 nois Geol. Survey Rept. Inv. 50, pp. 45-46, 

 pi. 1, figs. 1-2. 



2. ZoNALO-sPORiTES viTTATUs Ibrahim, 1933, 

 Sporenformen des Aegirhorizonts, p. 41, pi. 

 6, fig. 45. 



Genus Monoletes (Ibrahim) 1933, 

 emend, S. W. and B. 



Plate 2, figures 17-17c 



Symmetry. — Spores apparently bilat- 

 eral, monolete. Mature forms evidently 

 have been modified considerably in post 

 tetrad maturation, and it is possible that 

 although the mature forms appear very 

 definitely bilateral, they may have arisen 

 from tetrahedral tetrads. 



Shape. — Elliptical to rounded lenticu- 

 lar in outline as viewed from the proxi- 

 mal side; of similar figure but of more 

 slender proportions in the plane of the 

 long axis viewed from the side ; the short 

 transverse axis shows a somewhat rounder 

 and shorter but notably flattened outline. 

 The distal surface oftentimes is marked 

 by two prominent grooves extending near- 

 ly the length of the spore with a well 

 rounded umbo between. Sometimes the 

 proximal side near the suture shows a 

 very slight prominence. On compression, 

 longitudinal folds frequently parallel the 

 distal grooves. 



Si^e. — Spores relatively large, varying 

 from slightly over 100 microns to as 

 much as half a millimeter in length. 



Ornamentation. — Surfaces generally 

 minutely granulose appearing quite 

 smooth at low magnification; sometimes 

 glistening in reflected light. Emphytic 

 marking is evenly distributed except at the 

 extreme base of distal grooves, which are 

 more smooth. 



Haptotypic features. — ^When closed the 

 proximal suture is a very narrow linear 

 groove, generally lacking marginal dis- 

 tinction, though the lip area may be very 

 slightly upraised. The most noteworthy 



and diagnostic feature is the slight angu- 

 lar deflection of the suture fine near the 

 middle. Although inconspicuous and 

 sometimes hardly evident it seems to be 

 universally present. It may constitute the 

 sole remnant of a third vestigial ray in a 

 fundamentally trilete suture pattern. Very 

 weakly developed termini of arcuate rid- 

 ges are occasionally resolved at the two 

 ends of the functional suture line. The 

 suture opens to form a sharp taper- 

 pointed lenticular slit. The distal grooves 

 have no connection with haptotypic struc- 

 tures. 



Spore coat. — The exospore consists of 

 a layer of varying thickness ; the proxi- 

 mal side and the center of the distal 

 umbo are as much as 15 or 18 microns; 

 the thinnest is at the base of the distal 

 grooves on either side of the umbo where 

 it may be less than 5 microns. An even 

 gradation exists between these extreme 

 areas and in normally compressed spores 

 the exospore thickness at the margin is 

 intermediate between the extremes. The 

 endosporal membrane is frequently evi- 

 dent as a crumpled translucent sack less 

 than a micron in thickness, sometimes 

 shrunken from the exospore at the spore 

 margin. The umbo and distal grooves, 

 when present, have the appearance of 

 functioning as a harmomegathus. 



Affinity. — Spores of this character dis- 

 tinguish a pteridospermic plant alliance 

 probably largely coextensive with the Me- 

 duUosaceae. They are characteristic of 

 all genera placed in the Whittleseyinean 

 sub-tribe (see Halle, 1933). The only 

 aberrant feature is the lack of distal 

 grooves in spores of Codonotheca; spores 

 of all other genera now assigned to this 

 alliance possess them. Codonotheca spores 

 are otherwise entirely characteristic of 

 Monoletes and when such spores are 

 found isolated they probably should be 

 assigned to Monoletes since there well 

 may be other types in addition to Codon- 

 otheca that also may lack distal grooves 

 and umbo. Spores of Codonotheca empha- 

 size the non-essential character of these 

 specialized distal structures. 



Remarks. — Much of the previous dis- 

 cussion is based on comparative study of 

 spores in Dolerotheca and Codonotheca 

 by Schopf from petrified and compression 

 material as well as from spores isolated 

 by maceration of coal. It has thus been 



