Three new Psammothidium species from lakes of Olympic and Cascade Mountains in Washington State, USA Author Enache, Mihaela D. Academy of Natural Sciences, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103 Author Potapova, Marina Academy of Natural Sciences, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103 Author Sheibley, Rich U. S. Geological Survey, Washington Water Science Center, 934 Broadway, Suite 300, Tacoma, WA 98402 Author Moran, Patrick U. S. Geological Survey, Washington Water Science Center, 934 Broadway, Suite 300, Tacoma, WA 98402 text Phytotaxa 2013 2013-08-29 127 1 49 57 http://dx.doi.org/10.11646/phytotaxa.127.1.8 journal article 5577 10.11646/phytotaxa.127.1.8 84eadb24-4c2c-4317-b068-c12776220192 1179-3163 5085461 Psammothidium alpinum Potapova & Enache sp. nov . ( Figs 9–21 , 40–44 ) Valvae linearae ellipticae, ovalis, 6.3–9.1 µm latae, 14.6–30 µm longae. Raphovalva cum area axialis angusta linearis versus, area centralis rectagularis. Raphe recta poris centralibus unciformis, termini distale punctiformis. Araphovalva cum area axialis angusta, area centralis circularis, irregularis, 1/2 valvae lata. Striae transapicales paulo radiatae, 22–25 in 10 µm cum striae breviores intercalares. Areolae rotundae, grossae, 25 in 10 µm . Valves linear-elliptic to oval, 6.3–9.1 µm wide, 14.6–30 µm long. Raphe valve with narrow linear axial area and rectangular-irregular central area. Raphe straight with hook-like proximal pores, drop-shaped distal endings ( Figs 10, 11, 13, 15, 16, 20 ). Rapheless valve with narrow axial area, irregular, rounded central area, occupying about ½ of valve breadth ( Figs 9, 12, 14, 17–19, 21 ). Transapical striae slightly radiate, 22–25 in 10 µm , with shortened marginal striae present (figs 41, 43). Areolae coarse, round, 25 in 10 µm ( Fig. 44 ). Type:— USA . Washington : Cascade Mountains , Snow Lake , 46.7576° N , 121.6982468° W , lake sediment (2–2.5-cm depth core interval; lake maximum depth 9.75 m ), collected 07 October 2009 , collection WACA019 , (Circled specimen ( Figs 9, 10 ) on slide GC64862 , accession # GC64862 ( ANSP !), holotype , designated here ; circled specimens on slide GC64863 ( ANSP !) and slide 84223 ( CANA !), isotypes, designated here ) . Etymology: —specific epithet refers to the occurrence of the new species in alpine, high elevation lakes. Psammothidium alpinum is similar to P. bioretii ( Germain 1957: 85 ) Bukhtiyarova et Round (1996: 9) in valve size and possession of relatively coarse areolae. It differs from P. bioretii by having more elongate, linear-elliptical valve shape with nearly parallel sides, and a straight central sternum (versus diagonal in P. bioretii ). In SEM ( Figs 40–44 ), P. alpinum displays a characteristic doublet of smaller areolae at the valve/ mantle junction and around the mantle ( Figs 40, 42 ). On raphe valves, the central area nearly reaches the valve margin and is bounded by 4–8 short striae. The raphe has characteristic hook-like widely spaced proximal endings ( Fig 40 ) that deflect in the same direction externally ( Fig. 40 ) and opposite internally ( Fig. 41 ). While P. bioretii has terminal raphe fissures curved to opposite sides, P. alpinum lacks terminal fissures, and distal external raphe endings are drop-shaped and do not expand beyond the last stria ( Fig. 41 ). Similar to P. bioretii , P. alpinum has coarse, round areolae visible in LM; a row of coarser areolae border the sternum and central area in LM ( Figs 10, 11 ) and a double row of finer areolae bordering the valve face-mantle junction is visible in SEM ( Figs 40, 42 ). Short intercalary striae are present along the valve margin and expand on the mantle ( Figs 41, 43 ). Psammothidium alpinum has similar valve shape as P. chlidanos ( Hohn et Hellerman 1963: 273 ) Lange-Bertalot (1999: 285) but it can be easily distinguished by its coarser striae and areolae visible in LM. P . alpinum was present in Hidden Lake NOCA (bottom sample, 2% relative abundance) and very rare in top samples from Snow and Stiletto lakes.