Ultrastructural studies of selected North American cretaceous megaspores ofminerisporites, erlansonisporites, horstisporites,andricinospora,N. Gen.

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Abstract
The megaspores Minerisporites subcrassulus Tschudy, Erlansonisporites spinosus sp. nov., Horstisporiles harrisii (Murray) Potonié, and Ricinospora cryptoreticulata gen. et sp. nov. from the Maestrichtian Hell Creek Formation of south central North Dakota, U. S. A. are studied with light, scanning electron, and transmission electron microscopy. In this manner, it is possible to achieve a more complete understanding of the total complement of morphologic features than is possible by using light microscopy alone. These megaspores are composed of two basic wall layers: an inner thin, often lamellated exine, and an outer, often multizoned perine. The perine appears as a uniformly granular layer when intact spores are observed with the light microscope. Transmission electron microscopy demonstrates that the perine is composed of variously oriented sporonin bodies.