Plagiopyxis bathystoma Thomas, 1961

Diagnosis: Shell clear, transparent, circular or very slightly oblong in dorsal view. In lateral view, the test, strongly domed, is part of a circular segment of approximately 200°. The ventral side presents, in the anterior region, a very deep invagination. In ventral view, the pseudostome, in narrow fissure, is masked by the dorsal lip. The dorsal and ventral lips join laterally, forming two very distinct rectilinear commissures, giving the pseudostomal region a characteristic trapezoidal appearance. In apical view, the invagination of the ventral side appears in the form of a tongue whose edges are welded to the corners of the lips. The covering, smooth, very regular, transparent, often has a slight gray-slate tint. It is made up of reworked amorphous siliceous elements, with barely visible limits, assembled by a hyaline cement, very finely chagrined and punctuated.

Dimensions: Length 68-72 µm; width 66-70 µm; dorso-ventral (height) 45-49 µm; depth of ventral side invagination: 18-25 um.

Ecology: Soil. This species abounds in the mors of the subalpine level of the Pyrenees; it reaches its maximum density in the acid humus of Rhodopineraie (Néouvielle massif).