SHELL subtriangular or transversely oval; lateral margins forming an angle at the beak of about 90° to 110°. Ventral valve somewhat more depressed than the opposite: beak prominent, arched, not strongly incurved. Dorsal valve larger, declining with a gentle curve towards the margins: beak incurved.Hall's originally named the species Rhynchonella formosa in the aforementioned 1859 publication but that appears to have since been updated to Machaeraria formosa based on Karl Wilson's 2014 book "Field Guide to the Devonian Fossils of New York".
SURFACE marked by twenty to twenty-four simple angular plications on each valve, from two to four of which in the middle are coarser and depressed in the ventral valve, having a corresponding number abruptly elevated upon the dorsal valve; concentrically marked by fine closely arranged striae.
The Kalkberg formation is lower Devonian in age (Lockhovian to Pragian stage). I collected this specimen from a roadcut near Shoharie, NY.