Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis) Author Lobban, Christopher S. Division of Natural Sciences, University of Guam, Mangilao, GU 83823, USA e-mail: clobban @ guam. net clobban@guam.net text Micronesica 2015 2015 2 1 49 journal article 299054 10.5281/zenodo.12117576 9ec266f5-1dc7-4272-9fbc-67c7f2b0f5aa 0026-279X 12117576 Mastogloia emarginata Hustedt Figs 51–55 Section: Ellipticae Ref. illus.: Hustedt 1931 –1959, fig. 896; Pennesi et al. 2013, figs 65, 66 ( lectotype specimen) Samples: GU44R-2, GU44AU-1; GU53E-2; GU66F-4 ; GU55B-4 Dimensions: Length 18–20 µm; width 9–13 µm; striae 20–23 in 10 µm; partecta 2 in 10 µm. Diagnostics: Small oval valves with 3–4 concave partecta on each side, reaching the apex, pore on the outer side of each partectum distinctively visible in LM ( Fig. 54 , arrows). Longitudinal striae nearly straight, coarser than the transapical striae, resulting in rectangular areolae. Comments: Differs from M. ovulum Hustedt , which has finer, circular areolae, and partectal pores that are not evident in LM. As noted in the errata to Lobban et al. (2012) , the specimen given there in pl. 33, figs 9, 10 for M. ovulum was misidentified and is given here correctly as M. emarginata ; the specimen of M. ovulum posted on the web in its place is printed here as Figs 56, 57 ; see Jordan et al. 2009 –2015, /taxa_id/585541, for SEM images of M. ovulum . Besides the unique pores, M. emarginata differs from M. ovalis A. Schmidt in having partecta reaching the apex and from M. matthaei (see below) and M. stellae (Pennesi et al. 2013, figs 45–52, 57–60) in the number of partecta as well as characters of the areolae.