Diommatetras grossa Komura (2001: 77

Sims, Pat A., Williams, David M. & Ashworth, Matt, 2018, Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera, Phytotaxa 382 (1), pp. 1-56 : 30-32

Diommatetras grossa Komura (2001: 77 , figs 55–75, text-fig. 3) ( Figs 105–110 )

Type:— Japan: Miocene Morito Formation, “Km-5912…Calcareous nodules…collected from one of the serial rocky shoals submerged beneath the upper tidal level along the sand beach at Morito in the west side of the Miura Peninsula (Lat. 35° 16’ 06”N, Long. 139° 34’ 24”E, Text-fig.1)” ( Komura 2001: 70), “Km-5912 (4) = 14.8 X 129.1 (Fm39901) (holotype)” = Komura (2001: fig. 14).

Valves quadrate with two opposing poles narrower and longer than the other two, margins concave ( Fig. 105, 109 ), length 39μm, breadth 36.5μm ( Komura 2001: 77, gives 25.5–33μm long, 21.5–31.5μm breadth). At narrower poles short elevation with ocellus at its summit extends outwards ( Fig. 105 ). Valve centre oval, distinctly convex ( Figs 105, 106, 110 ), the longer axis lying towards shorter apices.A series of radially aligned costae link valve centre to apices and a regular row of short costae link the narrow mantle to expanded hyaline valve margin ( Figs 105, 109 ). Central area depressed covered externally with anastomosing costae forming irregular reticulate pattern, spines at junctions. Poroid areolae lie within anastomosing costae, the majority occluded by raised cribrum ( Fig. 107 ), occasional specialised pore present ( Figs 107, 108 , arrow). Areolae ca. 12 in 10μm. Rimoportulae 2, each positioned at base of longer axis of central area opening externally through long tubular spine ( Figs 105, 109 ), internally through a slit between raised lips ( Fig. 108 ).

Observations:— Diommatetras appears to be closely related to Amphipentas . For a more detailed account see Komura (2001: 77–80).

This description is based on specimens from Atlantic City well at 406 ft., New Jersey, USA.

Figures

FIGURES 105–110. Diommatetras grossa Komura (Atlantic City well, 406 ft, USA). Fig.105. Quadrangular valve tilted valve margins concave. Lying opposite are 2 elevations each with a rimmed ocellus at summit. Lying midway between elevations vale margin expands with a submarginal stout spine, the opening of a rimoportula present. Valve centre convex with a depressed central area.; scale bar = 10 μm. Fig.106. Valve interior with radial rows of discrete poroid areolae extending from small depressed central area; scale bar = 10 μm. Fig. 107. Anastomosing costae enclosing areolae occluded by cribra with the occasional specialised pore (arrow); scale bar = 2 μm. Fig. 108. Interior opening of submarginal rimoportula, cribra and specialised pore (arrow); scale bar = 2 μm. Fig. 109. Valve rotated showing valve mantle attached to expanded hyaline valve margin by costae; scale bar = 10 μm. Fig. 110. Valve flat with concave valve margins, long costae linking an oval valve centre to elevations, long stout hollow spine, a rimoportula, at opposing angles; scale bar = 10 μm.