Original Description: Valves linear at centre, shallower at the poles, tapering further towards the apices, length 20-25µm, breadth 10-15µm. Transapical ribs robust, mostly primary, few secondary and tertiary; 4-6 in 10µm. Striae parallel to each other and to the ribs, appear as simple holes through the basal siliceous layer; 10-20 in 10µm, 5-8 between (primary) ribs. Sternum central, linear, slightly raised; pore fields appear absent, although polar striae somewhat more compact than those composing valve surface.
Rimoportulae present, large slit (1—1.5µm), usually situated at a pole, often partly on mantle.
Cingulum partly known. Valvocopula, open band, attaching by crenulated lip overlaying ribs of valve; pars interior consisting of 2-6 distinct rows of poroids (which coalesce internally); ligula absent; septum extending from pars interior with small pore penetrating pole of band. Other bands not observed.
T. arceli is distinguished by its shape; in larger specimens the outline of the valve is more regular and less undulated than that of T. emarginatus (Ehrenb.) W. Smith (Williams 1987).
Type slide: BM 101138.
Type locality: Academician Ridge of Lake Baikal (53°44′48″ N and 108°24′34″ E); water depth 333m (core sample 5043).
Material examined: Academician Ridge of Lake Baikal (53°44′48″ N and 108°24′34″ E, core sample 5043, holotype, BM 101138; core samples 4706, and 5018); Amalat plateau, Transbaikal area, borehole 4712, depth 144.2m (Sample #1402 , ex G. Chernyaeva), Middle Miocene.
Notes: A comment in the Catalogue of Diatom Names concerning the locality of the images of this species suggests that “Type material perhaps also illustrated on fig. 3-9, according to text (caption contradictory)”. The plate legend text noted that all “illustrations of specimens from the Academician Ridge, Lake Baikal (53°44′48″ N and 108°24′34″ E), water depth of 333m, except Figure 2, specimen from the Amalat plateau, Transbaikal area”.
Reference: Williams et al. (2006)