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 Petroneis humerosa (Brébisson ex W. Smith) Stickle & D.G. Mann Figs 95–97 Ref. illus.: Peragallo & Peragallo 1897 –1908, pl. 27, fig. 20; Hustedt 1961 –1966, fig. 1702 (both as Navicula humerosa ); Witkowski et al. 2000 , pl. 101, figs 2, 3, pl. 102, fig. 3 Samples: GU44I-3 Dimensions: Length 45–60 µm, width 29–34 µm; striae 12 in 10 µm Diagnostics: Valves broad, linear, slightly rostrate. Strongly radiating striae with coarse areolae; short striae interspersed between longer ones along the central linear part of the valve. Comments: Similar to P. latissima Gregory and P. monilifera Cleve ( Hustedt 1961 –1966, figs 1701, 1699), but those have coarser striae. There are a number of small ultrastructural differences between Petroneis and Cosmioneis which together warranted their separation ( Round et al. 1990: 526 ); SEMs from a sample in the Davis collection from Saipan , CNMI ( Figs 96, 97 ), show the internal central raphe endings to be crozier- rather than anchor-shaped, suggesting that the Guam specimen is also Petroneis . However, C. delawariensis (Grunow ex Cleve) D.G. Mann ( Witkowski et al. 2000 , pl. 106, figs 1, 2) is very similar in LM.