Iridistrophia sp.

Mergl, Michal & Budil, Petr, 2019, Rhynchonelliform Brachiopods And Trilobites Of The ‘ Upper Dark Interval’ In The Koněprusy Area Devonian, Eifelian, Kačák Event; The Czech Republic, Fossil Imprint 75 (1), pp. 92-107 : 97

Iridistrophia sp.

Pl. 1, Figs 12, 13

M a t e r i a l. Two ventral valves (PCZCU 2269b,

PCZCU 2271).

D e s c r i p t i o n. The ventral valve is moderate in size, 15 mm wide and 11.5 mm long, weakly convex in transverse and axial profiles, thin-walled relative to shell size, widest at the hinge line. Ornamentation is parvicostellate, with 12 straight primary costellae originating at the umbo. The costellae do not branch and gently increase in size anteriorly. New costellae originate exclusively by intercalation and rapidly attain the size of primary costellae. Interspaces are wider than the costellae. Their floors are covered by fine concentric fila of subequal size (Pl. 1, Fig. 12b, c). The costellae crests are not crenulated. Anteromedianly, there are 10–11 costellae per 5 mm. Shell substance is impunctate.

R e m a r k s. The preserved shell is slightly deformed having partly broken flanks. Therefore it is not clear whether the deviation from bilateral symmetry is original or caused by fossilization. The shell resembles the moderate-sized specimen of Xystostrophia umbraculum (VON SCHLOTHEIM, 1820) , but costellae on the latter are crenulated even in small specimens. Iridistrophia HAVLÍČEK, 1967 is known from the Lochkovian to Lower Eifelian ( Jansen 2001) but Halamski (2009) and Halamski and Baliński (2013) referred Iridistrophia undifera ( SCHNUR, 1854) from the Upper Eifelian of Germany, Poland and Morocco to this genus. The shell is similarly shaped to Schuchertella GIRTY, 1904 but this genus has an extropunctate shell. The small specimen with triangular ventral muscle field (Pl. 1, Fig. 13) bordered by widely divergent dental plates may belong to the same species.

O c c u r r e n c e. UDI, sample TM 12.