. Bulletin of the Natural Histort Museum. Geology series. 156 M. MOHANTI AND BRUNTON Type species. designation. Genus ISOPOMA Torley, 1934 Terebratula brachyptycta Schnur 1853, by original * Diagnosis. Aseptirhynchid lacking adult dental plates, with dor- sal valve thickening confined umbonally and free, disjunct hinge plates extending from well-developed inner socket ridges. Ventral valve thick-walled with prominent teeth. There are no median septa in either valve. Comment. Below we describe or comment on the twelve species described as belonging to lsopoma, including one new species.
. Bulletin of the Natural Histort Museum. Geology series. 156 M. MOHANTI AND BRUNTON Type species. designation. Genus ISOPOMA Torley, 1934 Terebratula brachyptycta Schnur 1853, by original * Diagnosis. Aseptirhynchid lacking adult dental plates, with dor- sal valve thickening confined umbonally and free, disjunct hinge plates extending from well-developed inner socket ridges. Ventral valve thick-walled with prominent teeth. There are no median septa in either valve. Comment. Below we describe or comment on the twelve species described as belonging to lsopoma, including one new species. The name /. brachyptyctum has been used in Germany to include speci- mens resembling the lectotype of Schmidt (1941), which are longer than wide, as well as more equidimensional specimens commonly found in the Middle and Upper Givetian strata, typically to the east of the river Rhine, Germany. We provide here some sections taken from both forms but have insufficient information to be able to differentiate these forms clearly, other than by their exteriors. Other species, eg. /. orthoglossa (Torley) and /. ovale Xian & Jian, somewhat resemble the wide forms of /. brachyptyctum and are of similar age. Further studies of these faunas are required to resolve these taxonomical problems and the stratigraphical range of true /. brachyptyctum. Shell STRUCTURE. The shell structure of lsopoma (Figs 19-21) is poorly known: no primary layer has been seen in fresh condition, but the secondary fibres are relatively large and angular; being some- what rhomboidal in is characteristic of many Palaeozoic rhynchonellids. lsopoma brachyptyctum (Schnur, 1853) Figs 1-5, 19 1853 Terebratula brachyptycta Schnur: 178: pi. 23, fig. 6. 1934 lsopoma brachyptyctum (Schnur); Torley: 81, pi. 3, 12-15. figs. la K. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not
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