. Bulletin of the Natural Histort Museum. Geology series. . 3c Fig. 3 lsopoma brachyptyctum (Schnur). Dorsal, ventral, anterior and lateral views; Givetian Massenkalk. Bilveringsen, Germany; BD 12784, x3. 1941 lsopoma brachyptyctum (Schnur); Schmidt: 45, pi. 4, fig. 88. 1966 lsopoma brachyptyctum (Schnur); Biernat: 106, pi. 22, figs 1-9. Type specimen. The lectotype, selected by Schmidt (1941: 45, pi. 4, fig. 88), is from Im Kalk zu Blankenheim (Schnur, 1853: 178). Schmidt did not specify the precise stratigraphical level of this specimen, which is in the Schnur Collection at the Palaon
. Bulletin of the Natural Histort Museum. Geology series. . 3c Fig. 3 lsopoma brachyptyctum (Schnur). Dorsal, ventral, anterior and lateral views; Givetian Massenkalk. Bilveringsen, Germany; BD 12784, x3. 1941 lsopoma brachyptyctum (Schnur); Schmidt: 45, pi. 4, fig. 88. 1966 lsopoma brachyptyctum (Schnur); Biernat: 106, pi. 22, figs 1-9. Type specimen. The lectotype, selected by Schmidt (1941: 45, pi. 4, fig. 88), is from Im Kalk zu Blankenheim (Schnur, 1853: 178). Schmidt did not specify the precise stratigraphical level of this specimen, which is in the Schnur Collection at the Palaontological Institute. Bonn, Germany. However, the lectotype possibly came from the Ahrdorf Formation (Mohanti, 1972: 170), which is considered to be Middle Eifelian in age (see Paulus, Struve & Wolfart, 1963: 466, text-fig. 1). Diagnosis. Outline approximately equidimensional, with great- est width at about two-thirds of the length of the shell; ventral sulcation prominent, commonly containing two ribs and an addi- tional pair of ribs lateral to the sulcus; fold weakly developed. Material. German specimens from the Eifel region are: 3 speci- mens (SMF XVII 342b, XVII 342c and XVII Bi) from Bilveringsen; one specimen (SMF XVII1168a) from Schleddenhof; one specimen (SMF XVII 342k) from the Ahrdorf Formation at Gees; and 5 specimens (SMF XVII2420) from the Ahbach Formation at Hallert. In addition, unregistered specimens were kindly donated by the late Dr Struve from the upper part of the Lahr Member of the Ahbach Formation (Loc. St. 949) (BD 12782-83) and from the Massenkalk (Kohlenstein Member) of the Kohlenstein quarry at Iserlohn- Bilveringsen (BD 12784). Stratigraphical range. According to Schmidt (1941: 45), in the Eifel area of Germany lsopoma brachyptyctum ranges from Middle Eifelian (Ahrdorf Formation) to the Fleringen Schichten, which is now known to range from the Ahbach Formation (upper- most Eifelian) to the Curten Formation (Lower Givetian) (Paulus, Struve & Wo
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