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) Lobban, Christopher S. Micronesica 2015 2015 2 1 49 Hustedt Hustedt 1925 [232,606,510,535] Bacillariophyceae Mastogloiaceae Mastogloia GBIF,CoL Chromista Mastogloiales 6 7 Ochrophyta species emarginata  Section: Ellipticae Ref. illus.: Hustedt 1931–1959, fig. 896; Pennesi et al. 2013, figs 65, 66 ( lectotypespecimen) Samples: GU44R-2, GU44AU-1; GU53E-2; GU66F-4; GU55B-4 Dimensions: Length 18–20 µm; width 9–13 µm; striae 20–23 in10 µm; partecta 2 in10 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. ovulumHustedt, 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. ovulumwas misidentified and is given here correctly as  M. emarginata; the specimen of  M. ovulumposted on the web in its place is printed here as Figs 56, 57; see  Jordanet al. 2009–2015, /taxa_id/585541, for SEMimages of  M. ovulum. Besides the unique pores,  M. emarginatadiffers from  M. ovalisA. Schmidtin 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.