FIGURES 37–50 in Planothidium incuriatum sp. nov. a widely distributed diatom species (Bacillariophyta) and type analysis of Planothidium biporomum

FIGURES 37–50. Planothidium biporomum. SEM views. Savannah River, Georgia, U.S.A. Material ANSP G.M.C. 3521(3). Fig. 37. External view of rapheless valve. Fig. 38. Internal view of raphe valve. Fig. 39. External view of raphe valve. Fig. 40. Internal view of rapheless valve with a prominent cavum. Fig. 41. External detail of the central area of a rapheless valve with uni- to biseriate striae in the middle part of the valve. Fig. 42. External detail of a raphe valve with reduced striae forming a rectangular area. Striae composed usually by three to four rows of areolae. Fig. 43. Internal detail of raphe valve showing the proximal raphe ends. Fig. 44. External detail of extremity of the rapheless valve. Striae becoming triseriate near the valve mantle junction. Groups of three areolae present on the mantle at the end of each striae. Fig. 45. Internal detail of a rapheless valve end. Fig. 46. Internal detail of the helictoglossae. Figs 47–48. External details of raphe valves. Figs 49–50. Detail of cavum aperture. Note the extremities of the border attached to the neighbour striae. Scale bars: Figs 37–41 = 5 µm; Figs 42–43 = 4 µm; Figs 44, 46–48, 50 = 3 µm; Figs 45, 49 = 2 µm.