The genus Dictydium was created by Schrader (1797) for Cribrarialike forms lacking a cup. Rostafinski (1875) gave it its modern definition: i.e. having meridional costae which are joined at frequent intervals by fine, more or less parallel threads. He further created a genus Heterodictyon for a species (H. mirabile) which has ribs in the lower part and a Cribraria-like net in the upper. Massee in his monograph (1892) transferred Heterodictyon to Cribraria (C. mirabilis Mass.), pointing out that there is “every shade of transition between the two extremes,” and that Heterodictyon bienaszii Racib. i.e. ( Cribraria macrocarpa of the later monographs) “closely connects the genus Cribraria in the wider sense with Dictydium.” Jahn in 1901 described a variety ”anomalum” of Dictydium umbilicatum (i.e. D. cancellatum Batsch), with a rigid stem “ohne die hakenformige Aufhangung in das Sporenkorbchen”, with a rather long sporangium, always without a cup, with the ribs merging into a Cribraria-like net in the upper part, and with a more persistent silvery peridium than is found in the typical form. He studied this taxon for some years, and came to the conclusion that it was not more than a variety of Dictydium umbilicatum. Later Meylan (Bull. Soc. Yaud. 44: 295. 1908) raised it to specific rank ( Dictydium anomalum), mentioning a similar variation in presence or absence of the cup as occurs in D. cancellatum, and never finding any “formes transitoires vers D. umbilicatum”. He further was of opinion that D. anomalum would probably be identical with Rostafinski’s Heterodictyon mirabile. In 1911 Lister reduced D. anomalum Meylan to his var. alpinum of D. cancellatum. In Bull. Soc. Vaud. 57: 305. 1932 Meylan went a step further, and sank Dictydium cancellatum (Batsch) var. alpinum Lister into Dictydium mirabile (Rost.) Meylan. In a later paper wherein G. Lister describes D. rutilum (Journ. of Bot 71: 222, 1933), this author states that D. cancellatum var. albinum is clearly the same as Rostafinski’s species, adding that Meylan considered this variety worthy of specific rank. Dr G. W. Martin (private communication, shortly to be published), agrees with Meylan that this taxon merits specific rank.