Askepasma Laurie, 1986

Topper, Timothy P., Holmer, Lars E., Skovsted, Christian B., Brock, Glenn A., Balthasar, Uwe, Larsson, Cecilia M., Stolk, Sandra Pettersson & Harper, David A. T., 2013, The oldest brachiopods from the lower Cambrian of South Australia, Acta Palaeontologica Polonica 58 (1), pp. 93-109 : 98

Genus Askepasma Laurie, 1986

Type species: Askepasma toddense Laurie, 1986 ; Atdabanian ( lower Cambrian ), Todd River Dolostone , Northern Territory, Australia .

Emended diagnosis.—Shell strophic, subquadrate in outline and ventribiconvex; ventral valve weakly to moderately sulcate, with well−defined, high, apsacline to catacline interarea, lacking a homeodeltidium, pedicle callist present; dorsal valve with weak to strong fold; dorsal interarea well defined, low, planar, anacline to catacline; with well−developed, small apical homeochilidium; shell ornamentation consisting of irregular concentric growth lines, microornamentation consisting of close−packed polygonal pits that penetrate the entire shell.

Remarks.—Despite the uncertainty surrounding the family, Askepasma does display a number of similar morphological characteristics to “cryptotretid” genera, Aldanotreta , Cryptotreta , and Dzunarzina . However, all three genera are monotypic and the detailed morphology of their respective type species is generally poorly known. Aldanotreta sunnaginensis Pelman, 1977 and Cryptotreta neguertchenensis Pelman, 1977 have only been documented from a few adjacent localities on the Siberian Platform and Dzunarzina elenae Ushatinskaya, 1993 from a single locality in western Mongolia with each species based on only a handful specimens. Discrimination between taxa is predominantly related to shell shape, inclination of ventral and dorsal interareas and the anterior commissure. For example, Cryptotreta and Aldanotreta are typically both transversely ovate, however, Aldanotreta is characterised by a broad sulcus and an apsacline ventral interarea whereas Cryptotreta is rectimarginate and with an orthocline ventral interarea ( Pelman 1977; Laurie 2000). Askepasma is easily distinguished from all three genera by its overall shell shape, sulcation and ornamentation. Askepasma differs from Aldanotreta in possessing a low, dorsal interarea and a distinct micro−ornament of irregularly arranged polygonal pits ( Fig. 2C 2). Askepasma is similar to Aldanotreta in that it is also invariably plicate, displaying a shallow and somewhat subdued fold in the dorsal valve (see Laurie 2000: fig. 86: 4c) similar to specimens of Askepasma toddense ( Fig. 3). Dzunarzina bears a striking resemblance to Askepasma , the strong morphological similarities between the two genera has previously been noted by Williams et al. (1998), who suggested a possible synonymy of Dzunarzina with Askepasma . The distinctive polygonal ornament possessed by Askepasma has not been observed on specimens of Dzunarzina (Galina Ushatinskaya, personal communication 2011) and Dzunarzina also does not typically display a fold or sulcus, unlike specimens of A. saproconcha sp. nov. ( Figs. 4, 5), however, lack of adequate material makes detailed comparison difficult.