(Haeckel)
Diagnosis: Shell lenticular, strongly compressed, ratio of longitudinal to sagittal to lateral diameters = 6:5:4. Free margins of two boat-shaped valves, dentate nearly in whole perimeter, in one lateral border of each valve 11 or 12 very large conical teeth, largest near half as high as valve. On aboral hinge 2 divergent, very large horns, four-sided pyramidal, acute, straight, with a few basal pores. Dorsal horn (of smaller valve) somewhat shorter than ventral. Apical distance of both horns somewhat greater than their length, about half length of shell. In half frontal perimeter (along one border of each valve) 32-34 pores, in half sagittal perimeter 34-38, in half equator 30-33. Pores smaller near girdle-fissure, irregularly quadrangular, in longitudinal rows, separated by meridional crests, converging towards both poles of main axis.
Length (without horns): 0.24-0.26 mm.