Mamatia retracta (Popov, 1980)

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 : 154-155

Mamatia retracta (Popov, 1980)

Fig. 11 .

Myotreta sp. ; Biernat 1973: 85, pl. 15: 6–8.

Paratreta retracta sp. nov.; Popov (in Nazarov and Popov) 1980: 95, pl. 25: 1–6.

Mamatia retracta (Popov) ; Popov and Holmer 1994: 128, fig. 102.

Mamatia retracta (Popov) ; Holmer and Popov 2000:127, fig. 69, 3a–g.

Material.—Total of 57 ventral and 105 dorsal valves. Figured ventral valves: RM Br133830 (W = 1.19, L = 0.88, H = 0.66), RM Br133832, RM Br133833 (W = 0.57, L = 0.45, H = 0.32), RM Br133834, RM Br133835; dorsal valves: RM Br133828, RM Br133829 (W = 0.70, L = 0.50, WI = 0.34, LS = 0.40, BS = 0.22), RM Br133831 (W = 0.93, L = 0.78, WI = 0.48, WM1 = 0.63, LM1 = 0.37, LS = 0.56, BS = 0.26).

Diagnosis.—As for genus.

Description.—Shell transversely suboval, around 74–84% as long as wide (N = 4). Ventral valve broadly conical, around 71–75% as high as long (N = 2) with maximum height at umbo. Ventral pseudointerarea procline to almost catacline, bisected by poorly defined intertrough. Pedicle foramen at the end of very short external pedicle tube, enclosed within larval shell. Apical process slightly ridged anteriorly.

Dorsal pseudointerarea low, orthocline, occupying around 49–52% of valve width (N = 2). Dorsal median septum low, extending for around 72–80% of valve length. Dorsal median buttress and cardinal muscle scars variably developed. Larval shells of both valves well defined, transversely suboval, around 0.22 mm wide, surrounded by raised rim.

Discussion.—The specimens from Poland agree closely with the types from the Chingiz Range, as well as those described by Popov and Holmer (1994) from the South Urals. The only difference is that the dorsal median septum is somewhat lower and the upper septal rod is not as well defined as in the Asian material. The median septum of the ephippelasmatids usually shows some degree of intraspecific variation.

Figures

Fig. 11. A–L. Mamatia retracta (Popov). A. Dorsal valve RM Br133828, exterior, × 40. B. Dorsal valve RM Br133829, interior, × 50. C. Ventral valve RM Br133830, exterior, × 32. D. Dorsal valve RM Br133831, interior, × 27. E, H, I, K. Ventral valve RM Br133832, exterior (E, × 75), oblique posterior view (H, × 40), oblique lateral view (I, × 75), detail of larval shell (K, × 162). F. Ventral valve RM Br133833, oblique lateral view, 62. G, J. Ventral valve RM Br133834, interior (G, × 45) and detail of apical process (J, × 195). L. Ventral valve RM Br133835, detail of larval shell, × 150. All specimens from the Tremadoc chalcedonites, Wysoczki.