The thecal form of Monograptus argutus Lapworth and M. leptotheca Lapworth is similar to that of M. incommodus Toernquist, the type species of Pribylograptus Obut & Sobolevskaya; their thecae are geniculate and have introverted and laterally expanded apertures, and M. leptotheca has in addition apertural hoods. The relationships of these species are discussed.