Corals with horse-shoe disseptiments and resting on them trabecular fans, formerly included by the writer in the subfamily Pachyphyllinae Stumm, are now referred to the family Thamnophyllidae Soshkina. The systematic division of this family is given. An analysis of correlation between the number of septa and the diameter of calice or of tabularium (n/d or n/t) in genera Thamnophyllum Penecke, Macgeea Webster, Pexiphyllum Walther and Pachyphyllum Edward & Haime has made possible the determination of the range of individual variability and the
elucidation of evolutionary tendencies within the quoted genera. The coefficient of correlation for particular species is of diagnostic value and may constitute their stratigraphical index. It has been established that species previously described and referred (Różkowska, 1953, 1956) to the genera - Pseudoacervularia Schluter and Pachyphyllum Edwards & Haime should be assigned to genus Pachyphyllum. Within this genus four groups of species, with peculiar, similar coefficients of correlation, should be differentiated. Conclusions concerning speciation have been deduced from biometrical treatment and from ontogenic and morphological studies. A description is given of the phyletic and chronological evolution of Thamnophylliae. In addition to material from the Holy Cross Mts. specimens collected at Dębnik and in the Sudeten were used by the writer for the present work.