Specimens of a Didymium collected at Endegeest near Oegstgeest, a suburb of Leiden, on holly leaves, were put aside by Prof. Dr. W. K. H. Karstens as being near to Didymium squamulosum (Alb. & Schw.) Fries, but not identical with it. Some of the specimens were collected in August 1944 by Dr. S. J. van Ooststroom, whereas several other ones were collected in October of the following year by Prof. Karstens at the same locality; they are all very similar, and remarkable in the smooth white calcareous crust, which is distant from the membranous inner part of the peridium, and in the rather dark spores, which are nearly all encircled by a thin, sometimes fragmentary ridge. Comparison with a large number of specimens of D. squamulosum has convinced me that the specimens collected at Endegeest are indeed distinct from that species. LISTER, in a footnote to D. squamulosum (3rd ed. 1925, p. 118), mentions a form collected on holly leaves, but the description and figure prove that this is plainly D. squamulosum, and certainly not identical with the above mentioned specimens. The specimens from Endegeest are not identical with D. praecox de Bary either. The latter is described by Lister “as so inconstant that the name cannot be applied to mark even a variety”. However, D. praecox was described by Berlese in Saccardo (Syll. 1306) and by Massee (Mon. p. 223) (the two descriptions, probably based on that given by Rostafinsky, which was not seen by me, are practically identical) as possessing a double peridium. Study of a duplicate of de Bary’s type specimen in the Rabenhorst “Fungi Europaei” collection no. 367, 1861, preserved at the Rijksherbarium at Leiden (no. 910243-676), shows this to be D. squamulosum, as the crystalline lime crust closely adheres to the membranous inner layer of the peridium, a condition which is characteristic of this species; this is seen quite clearly at the time of dehiscence, as the two layers break away simultaneously. The spores were found by me to be 10-11 µ in diam., and not 8—9 µ, as they are said to be in Massee’s description (which, however, comes within the range allowed for the spores of this species by Lister and by Martin in their monographs, viz. 8-11 µ), and they are spinulose; some of the dark spinules are grouped in clusters, whereas the remaining ones are unevenly and sparingly scattered between these clusters. In the specimens collected at Endegeest the crystalline lime layer of the peridium, as stated above, is distinctly separated from the membranous inner layer, the latter, moreover, is often provided with light brown areolae, a feature which is seen also in D. nigripes and in D. melanospermum, but which I myself have not met with in D. squamulosum. However, Lister describes the inner peridium of the latter as “sometimes mottled with red-brown towards the base”; this, therefore, is a point which deserves further study. Other noteworthy points are that the spores of the new species are provided with a ridge and that the spinules are not arranged in clusters.