Heterotrypa

COMPARISON

DIAGNOSIS. — Colonies frondose, ramose or less commonly encrusting. Autozooecial walls can be extremely variable in thickness. Zooecial boundary is a conspicuous dark line in inner exozones and in a broad zone of abutting laminae or completely obscured in outer exozones. Walls generally are amalgamate in appearance. Diaphragms are generally few in endozones, but are moderately abundant in some species. In exozones, diaphragms are closely and regularly spaced, thin, planar and perpendicular to the zooecial walls. Intermonticular mesozooecia range from abundant and regularly arranged to scattered or absent. Mesozooecia develop commonly moniliform chambers at proximal ends and tend to become smaller or are terminated distally within exozones. Diaphragms in mesozooecia noticeably thicker and more closely spaced than zooecial diaphragms. Acanthostyles are at least two kinds within the genus, regular acanthostyles limited to exozone, and the endacanthostyles originating in both endozone and exozone. Endacanthostyles occur in all species. Monticules generally have a central cluster of a few mesozooecia than those in the intermonticular area.

The genus Heterotrypa Nicholson, 1879 differs from the genus Leioclema Ulrich, 1882 by abundant diaphragms in autozooecia, more angular apertural shape and two kinds of acanthostyles.

OCCURRENCE. — Middle Ordovician-? Devonian; worldwide.

TYPE SPECIES. — Monticulipora frondosa d’Orbigny, 1850 by subsequent designation (Utgaard & Boardman 1965). Cincinnatian, Upper Ordovician; North America.