Multivariate morphometric analysis was applied for differentiation of closely related species and evaluation of intra- and interspecific variation in Manipora from the Selkirk Member, Red River Formation, in southern Manitoba. Seven morphological characters were quantified in transverse thin sections of 46 coralla and statistically tested for selecting effective characters in discriminating species. Cluster analysis was performed on a raw data matrix coordinated with 46 coralla by three selected characters. Two major clusters on the resulting dendrogram were regarded as morphospecies, following comparative examination of the coralla using serial sections. Cluster analyses were also conducted on principal component score matrices obtained from the raw data set coordinated with 46 coralla by all seven characters, and from an experimental data set including the 46 coralla plus two replicates of each and six of the characters. The results agree closely with the first cluster analysis, but discrimination of morphospecies was slightly degraded. The validity of two morphospecies recognized in the first cluster analysis was verified by discriminant analyses, descriptive statistics, and bivariate plots. The results show that tabularium area is the most meaningful character for distinguishing these morphospecies; ranges of variations of the other six characters overlap between morphospecies.

Another cluster analysis like the first was performed, but with the addition of 11 type specimens and reference coralla of Manipora species from the Upper Ordovician of southern and northern Manitoba and Texas. Based on this analysis, together with comparative examination of thin sections, the two morphospecies are identified as valid species: M. amicarum Sinclair, 1955 and M. manitoba (Sokolov, 1955). Manipora magna Flower, 1961 is considered to be a synonym of M. amicarum, while M. trapezoidalis Flower, 1961 and M. garsonensis Caramanica, 1992 are considered to be synonyms of M. manitoba, and the hypotypes of M. amicarum of Nelson (1963) are assigned to M. manitoba.