Siphonobolus uralensis ( Lermontova, 1933 )

Holmer, Lars E. & Biernat, Gertruda, 2002, Urban and Peri-urban small and medium-size Enterprise Development for sustainable Vegetable Production and Marketing Systems, Acta Palaeontologica Polonica 47 (1), pp. 141-156 : 147

Siphonobolus uralensis ( Lermontova, 1933)

Fig. 4 .

Siphonotreta uralensis Lermontova (in Lermontova and Razumovskij), 1933: 202, pl. 1: 7–13.

Siphonotreta cf. verrucosa (Eichwald, 1840) ; Biernat 1973: 107, pl. 30: 1–5.

Siphonobolus uralensis ( Lermontova, 1933) ; Popov and Holmer 1994: 82, fig. 73 [full synonymy]

Material.—Total of 21 ventral and 7 dorsal valves. Figured ventral valves: RM Br133780, RM Br133781, RM Br133785; dorsal valves: RM Br133779, RM Br133783, RM Br133784.

Diagnosis.—See Popov and Holmer (1994: 82).

Description.—Shell subequally biconvex and elongate subcircular, around 105–120% as long as wide (N = 2). Ventral valve moderately and evenly convex in lateral profile, less than 20% as high as long (N = 1), with maximum height anterior to the beak. Ventral pseudointerarea very low, apsacline and poorly defined laterally. The pedicle foramen is subcircular, about 0.06–0.1 mm wide. Ventral interior with long, cylindrical, internal pedicle tube.

Dorsal valve moderately convex in lateral view, less than 15% as high as long (N = 1), with maximum height placed somewhat posterior to mid−length. Dorsal pseudointerarea undivided, slightly anacline and strongly raised above valve floor. Dorsal interior with pair of large, but poorly defined, central muscle scars.

Shell surface finely pustulose (less than 10 µm across), with rows of thin and hollow spines of about equal size (about 40–70 µm across). Larval shells of both valves poorly defined.

Discussion.—The Polish material is almost identical with Siphonobolus uralensis (Lermontova) redescribed from the Early Ordovician of the South Urals by Popov and Holmer (1994). It differs mainly in being somewhat more subequally biconvex, rather than ventribiconvex, and in having a somewhat smaller pedicle opening, but these are commonly variable features in siphonotretid species. A comparative discussion of this species was given by Popov and Holmer (1994).

Figures

Fig. 4. A–L. Siphonobolus uralensis (Lermontova). A, G. Dorsal valve RM Br133779, interior (A, × 15) and oblique lateral view (G, × 23). B. Ventral valve RM Br133780, exterior, × 19. C, D, L. Ventral valve RM Br133781, oblique lateral view of exterior (C, × 33), posterior view (D, × 36) and detail of pedicle opening (L, × 80). E, H, J. Ventral valve RM Br133782, oblique lateral view of interior (E, × 28), detail of posterior margin (H, × 100) and detail of pedicle tube (J, × 70). F. Dorsal valve RM Br133783, oblique lateral view of exterior, × 26. I. Dorsal valve RM Br133784, oblique lateral view of interior, × 37. K. Ventral valve RM Br133785, detail of pedicle tube, × 55. All specimens from the Tremadoc chalcedonites,Wysoczki.