. Bulletin of the British Museum (Natural History), Geology. . Figs 1, 2 Productellina fremingtonensis Reed, from the Pilton Beds of Fremington, north Devon, probably of lowest Tournaisian age. Specimens in the Sedgwick Museum, Cambridge. Fig. 1, latex mould of the dorsal valve exterior of the holotype described by Reed (1943) and figured by Whidborne (1898: pi. 22, fig. 2). E287, X2. Fig. 2, internal mould of a ventral valve showing weak ribbing and the internal openings of paired spines (arrowed). H1665. x2. Cambridge, reveals that this genus belongs in the Productini- nae. Its elongate outl
. Bulletin of the British Museum (Natural History), Geology. . Figs 1, 2 Productellina fremingtonensis Reed, from the Pilton Beds of Fremington, north Devon, probably of lowest Tournaisian age. Specimens in the Sedgwick Museum, Cambridge. Fig. 1, latex mould of the dorsal valve exterior of the holotype described by Reed (1943) and figured by Whidborne (1898: pi. 22, fig. 2). E287, X2. Fig. 2, internal mould of a ventral valve showing weak ribbing and the internal openings of paired spines (arrowed). H1665. x2. Cambridge, reveals that this genus belongs in the Productini- nae. Its elongate outline, dorsal valve lamellae (Fig. 1), rather fine ventral ribbing and apparently single pair of flanking spines (Fig. 2) indicate an affinity with Productina. Productellina differs from Devonoproductus by apparently lacking spines over the entire ventral valve. As a member of the Productininae it is probably only slightly younger than Dorsirugatia. Thus we have an early division in this subfamily into two lineages of species; Dorsirugatia evolving into Argentiproductus while Productellina evolved into Produc- tina. In the mid Tournaisian of North America other elongate, weakly spinose and finely ribbed species evolved as Produc- tina sampsoni Weller, 1909, and in late Tournaisian rocks Productina parvula Winchell, 1863 appears. The genus con- tinued through the Visean and, if the record of Winkler Prins (1968) of P. pectinoides (Phillips) is correct, the youngest record is from the early Bashkerian in north Spain. The growth of long thin dorsal trails in this subfamily is characteristic. There is no evidence so far of ventral lamellae being as long, but we would not expect this. Dorsal valve growth involved no geniculation, but at all growth stages, after a length of a few mm, a short simple trail was composed of the margins of both valves. In order to accommodate the growing internal organs the geometry of the shell curvature necessitated periodical mantle regressions followed
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