FRUCTIFICATIONS FROM THE MAZON CREEK FLORA 



A ultimate, and continuing with n-2 and 



n-3, according to H. W. Pfefferkorn 

 (in press). The lamina has the same 

 designation as its main vascular strand 

 and in this way elements which are 

 morphologically equivalent will have 

 the same "n" designation even if their 

 outlines appear to be lobes on one spec- 

 imen, or part of a specimen, and pin- 

 nules on another. The use of a descend- 

 ing order in the numbering and describ- 

 ing of foliage elements in fossil ferns 

 has been used by many authors (summa- 

 rized by Raabe, 1966). The terminology 

 proposed in this paper differs by includ- 

 ing midveins and lateral veins in the 

 count of orders . 



The formal designation proposed here is especially helpful in the form- 

 genus Sphenopteris and a few other highly dissected forms, such as Stellatheca, 

 which show a high variability in the division of their foliage. It has not been 

 applied to the other genera in this report because there exists no problem in the 

 designation of the laminate units in the form-genera Alloiopteris and Pecopteris . 

 In Myriotheca it would be quite helpful but is at present not applicable because 

 the veins are not visible in the specimens. 



Text fig. 2 



Proposed designation of dif- 

 ferent parts of the lamina of 

 Stellatheca and Sphenopteris , 



Acknowledgments 



The specimens for this study were kindly loaned to the senior author by 

 Dr. F. M. Hueber and Dr. S. H. Mamay, Washington, D. C, Mr. R. L. Leary, 

 Springfield, and Dr. E. S. Richardson, Chicago. The electron micrographs of the 

 spores were made by Dr. R. Blaschke, Munster, Germany, whose help is very much 

 appreciated. Some of the figures were specially prepared by Margaret S. Whaley. 

 Thanks are due to Dr. C. A. Arnold, Ann Arbor, for helpful discussions at an early 

 stage of the project. 



Genus STELLATHECA Danze, 1956 



Stellatheca is regarded as a fern fructification. According to Danze (195 6), 

 the genus Stellatheca can be described as follows. The sori of Stellatheca consist 

 of 6 to 15 free sporangia, with most of the sporangia forming a circle or an ellipse 

 around 1 to 3 centrally located sporangia. Sori are attached to the abaxial lami- 

 nar surface of pecopterid to sphenopterid pinnules between the midvein and the 

 margin or at the margin near the end of a lateral vein. Sporangia are ovoid, and 

 a longitudinal dehiscence is found on the outer face of peripheral sporangia. De- 

 spite the lack of an annulus, a terminal zone of isodiametric cells resembles an 

 apical plate oriented toward the margin of the soral circle. The sporangial wall 

 consists of longitudinal rows of elongate cells, and sporangia are attached to a 

 receptacle by a slightly tapered base. 



To the above may be added spore data from this study: Spores are trilete 

 and subcircular to circular. Laesurae are usually indistinct and extend three- 

 quarters the length of the spore radius. Ornamentation consists of conate projections 



