Cover image:

Detailed view of a bryozoan in oblique section; in this specimen a large amount of the zooecia (elongated purple pores) are filled with calcite cement. This organisms were part of a diverse reef community in the Olinalá Formation (late Permian). Microphotograph taken with polarized light and analized with 1/4 lambda quartz wedge. Horizontal axis 2.5 mm. Courtesy of Edgar Juárez Arriaga