Stenotheca, Salter, 1872

Skovsted, Christian B. & Peel, John S., 2007, Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of western Newfoundland, Acta Palaeontologica Polonica 52 (4), pp. 729-748 : 734-736

Stenotheca ? sp.

Fig. 4C.

Type species: Stenotheca cornucopia Salter, 1872 .

Material.—NRM−684 and five additional specimens from sample JSP1982−01.

Description.—Shell high, cap−shaped and laterally compressed. Coiled through about 90 °. Aperture elongated oval (width about 60% of length) and lying in a single plane. The greatest elongation of the aperture is shifted about 10 ° anticlockwise (in dorsal view, Fig. 4C 2 ) from the apex. Protoconch small and cap−shaped.

Discussion.—This species is known from a few internal moulds, only one of which is reasonably complete. No evidence of the external morphology is preserved and the available specimens does not preserve any small scale internal features. The slender, open coiled shell and lateral compression are reminiscent of the genus Stenotheca . The type species of this genus, S. cornucopia Salter, 1872 , is not well known ( Bengtson et al. 1990; Skovsted 2004), but other species referred to Stenotheca (see Parkhaev in Gravestock et al. 2001: 182) have extremely narrow apertures, usually with a sub−apical flexure. The specimens from Newfoundland described above are questionably referred to Stenotheca , although the aperture lacks sub−apical flexure and is wider than in most specimens assigned to this genus. A specimen of genus incertum et species incerta C from the Middle Cambrian of Morocco ( Geyer 1986: pl. 3: 46) appears to resemble the Newfoundland material, but the available illustration precludes detailed comparison.

The slight asymmetrical coiling of the best preserved specimen may be a consequence of deformation, as indicated by occasional deformation of acrotretid brachiopods and the problematic Salterella sp. from the same suite of samples. Asymmetrical coiling is characteristic of some helcionelloids (e.g., Aldanella Vostokova, 1962 , Archaeospira Yu, 1979 , Pelagiella Matthew, 1895 ), but also occurs occasionally in otherwise planispiral species (e.g., Oelandiella korobkovi Vostokova, 1962 ; Gubanov and Peel 2000).

Figures

Fig. 2. Brachiopods from the Lower Cambrian, Forteau Formation (Western Newfoundland). A, B. Eoobolus priscus (Poulsen, 1932). A. NFM−662, exterior view of incomplete ventral valve. B. NFM−663, ventral valve interior with pseudointerarea. C. Ventral valve of Eothele sp., NFM−664 from ICS 1421. D, E. Acrotretid indet. D. NFM−665, ventral valve exterior. E. NFM−666, dorsal valve exterior. F, G. Micromitra bella (Billings, 1872). F. NFM−667, ventral valve interior. G. NFM−668, dorsal valve interior. H, I. Obolella crassa (Hall, 1847). H. NFM−669, fragmentary ventral valve interior. I. NFM−670, fragmentary dorsal valve interior. All specimens from JSP 1982−01 unless otherwise stated. Scale bars 500 ̊m.