Diorygma Biernat, 1961

Category of architectural design: 2.61. U-shaped borings.

Diagnosis.-A boring in the pedicle valve of Atrypa zonata Schnur (pl. III, fig. 1a,b) consisting of minut, smoth , nearl y V-shaped tube. widening slightly anteriorly, burrowed through all the shell substance and all the length of a prominent internal ridge, placed on the lateral sides of the pedicle muscle area. The tubes are opened to the interior of the brachiopod shell by two apertures lying on the anterior, free extremity of the ridge.