Amphitetras elegans Greville (1866: 9

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 : 27

Amphitetras elegans Greville (1866: 9 , pl. 2, fig. 24) ( Figs 100–104 )

Synonyms:— Triceratium elegans (Greville) Grunow in Van Heurck (1883: pl. 109, fig. 1) Biddulphia elegans (Greville) Boyer (1900:

717) Odontella elegans (Greville) M. Peragallo (1903: 687) non Odontella elegans (Van Heurck) De Toni (1894: 869) Type:—“Monterey deposit; L. Hardman, Esq.” ( Greville 1866: 9; Williams 1988: 7, pl. 6, figs 4, 8, “Monterey L. H. no. 31”, BM 10007!,

holotype!).

Valves quadrangular with rounded apices ( Fig. 101 ), length of margin 70–100μm. A slightly raised triangular elevation with outwardly aligned ocellus positioned at apices ( Fig. 102 ), diameter c. 10μm, at its summit. Hyaline margin at base of each elevation creates a square valve face ( Fig. 101 ). Valve face weakly convex with small concave central area ( Fig. 101 ). Valve margin expanded, hyaline with raised border ( Fig. 102 ). Valve punctured by poroid areolae arranged in rows radiating from valve centre ( Fig. 104 ). Ridged papillae present between areolae ( Figs 102, 103 ). Poroid areolae occluded by cribra with scattered specialised pores present. Rimoportulae 4, each in submerged position midway between ocelli, external opening through short, buttressed spine ( Fig. 103 ).

Observations:— The description above is based on material from San Redondo, California, USA (Miocene).

Figures

FIGURES 95–100. Amphitetras antediluviana Ehrenberg (Port Shepstone, Natal, South Africa). Fig. 95. Quadrangular valve exterior with broadly rounded apices and attached valvocopula; valve surface covered in anastomosing costae, valve centre depressed; scale bar = 10 μm. Fig. 96.Anastomosing costae with surface spinules enclosing poroid areolae mostly occluded by cribra with occasional specialised pores (arrow); scale bar = 2 μm. Fig. 97. Mantle view of valve with barely raised elevations and attached girdle bands; scale bar = 10 μm. Fig. 98. Detail large rimmed ocellus, distally inclined, cribra and specialised pore; scale bar = 2 μm. Figs 99–100. Reproduction of Ehrenberg’s original drawing of Amphitetras antediluviana (Ec 100, housed in Berlin: http://download.naturkundemuseum-berlin. de/Ehrenberg/Ec%20Drawings/Ec%20draw%20001-999/Ec%20draw%20100-199/Ec%20dr%200100.jpg), the published illustration appearing in Ehrenberg (1854: pl. 19, fig. 19).

FIGURES 101–104. Amphitetras elegans Greville (San Redondo, California, USA). Fig. 101. Quadrangular valve exterior with four slightly raised triangular elevations at apices, depressed valve centre and radial rows of poroid areolae; scale bar = 10 μm. Fig. 102. Elevation with opening of ocellus, remains of porelli on margin, extended hyaline valve margin with raised border; scale bar = 2 μm. Fig. 103. Midway between apices, buttressed opening of rimoportula, remains of cribra occluding poroid areolae, occasional specialised pore (arrow) and surface ridged papillae; scale bar = 3 μm. Fig. 104. Valve interior with radial rows of poroid areolae; scale bar = 50 μm.