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 Hagelstein Hagelstein 1939 [232,595,1628,1653] Bacillariophyceae Mastogloiaceae Mastogloia GBIF,CoL Chromista Mastogloiales 6 7 Ochrophyta species obliqua  Samples: GU66F-4 Dimensions: Length 13 µm, width 4.4 µm, striae ca. 25 in10 µm. Diagnostics: Small, rostrate valves with one partectum on each side (sometimes two, as shown by Hagelstein 1939), placed slightly obliquely across the central area. Comments: Comparable with  M. tenuisHustedt( Lobban et al. 2012, pl. 37, figs 6–8), which is not rostrate, has finer striae, and has two small tapering partecta bordering the larger partecta on each side, the chambers symmetrically placed (as in most  Mastogloiaspp.) and also has axial costae bordering the internal raphe-sternum. Also similar to  M. giekesiiCholnoky( Loir & Novarino 2013, pl. 13a), which is rostrate, has two chambers on each side (apparently never only one), symmetrically placed.