Cyphotrypa osgoodensis

• Zoarium Morphology: Massive
• Zoecia: Polygonal; thin-walled; acanthopores well developed
• Mesozooids: None
• Monticules: Low

Brown & Daly (1985):

• Diagnosis: Zoarium massive, with large polygonal zooecia, diaphragms sparse in endozone and numerous in exozone, no mesozooecia, and abundant acanthopores.
• Description: Single zoarium large, massive, or hemspherical (sp?), 4 cm high by 4 cm wide by 2.5 cm thick; surface worn locally but unworn in places, with conspecific overgrowth in one place. Several small low monticules. Zooecia polygonal, of varying shape, large, fanning gradually outward from base to reach surface directly. Intermonticular zooecia in peripheral exozone large (5.7 in 2 mm, 0.358 mm MZD; table 13), characterized by slightly thickened walls (0.015 mm ZWT), and numerous diaphragms set one-half to three tube diameters apart; endozone characterized by thin walls and absence of diaphragms.
  Diaphragms scattered throughout the inner part of the colony, which may represent exozone development, then absent for some distance before reappearing near the surface; straight, inclined, or curved, convex more commonly than concave; locally with short diaphragm-zooecia wall lining units.
  Mesozooecia absent. Acanthopores abundant (11 A1M), at most wall angles where they greatly exceed wall thicknesses, of medium size (0.044 mm MAD), and composed of concentric laminations with a large lumen. Typically appearing in exozone walls as translucent laminations sharply convex outward, occasionally with translucent rodlike centers, and generally extending only a short distance.
  Monticules not obvious in tangential views, consisting of a few megazooecia with thickened walls and acanthopores.
• Discussion: C. osgoodensis was previously reported (Perry and Hatin, 1960, p.703) only from the Osgood Formation (Silurian) in southeastern Indiana. Its presence in the Dillsboro significantly extends its range into older strata. Our specimen is characterized by large zooecia that agree with original measurements; Perry and Hatin reported 5+ zooecia in a 2-mm distance and few diaphragms in the zooecia, but they also reported that one of their paratypes had diaphragms generally more common in the basal third of the zoarium where they were two or three tube diameters apart. Our specimen has slightly more zooecia in 2 mm and has diaphragms common in the exozone; it is much larger than their specimens. In other respects, the specimens agree.
  Cyphotrypa osgoodensis is perhaps more closely related to C. waynensis Utgaard and Perry than any other Late Ordovician species. Utgaard and Perry reported zoarial development even larger than in our specimen. Their species has, however, much smaller zooecia, and it has diaphragms distributed completely throughout the zooecial tubes.

Perry & Hattin (1960):

• External description. – Zoarium free, hemispherical, up to 6 mm. thick and 16 mm. in diameter, or a laminate growth, having a maximum observed thickness of 7 mm., encrusting other fossils. Surface weathered, not revealing monticules or maculae, but locally showing slightly projecting acanthopores.
• Internal description. – In tangential section, zooecia polygonal, commonly 5- or 6-sided, rarely subround, with thin amalgamate walls; generally (12 of 20 measurements) five entire zooecia and part of sixth in 2 mm.; somewhat less commonly (8 of 20 measurements) four entire zooecia and portion of fifth in this distance; zooecia relatively uniform in size, except for a few conspicuously smaller young zooecia that typically are subpolygonal. Acanthopores small to medium-sized, noninflecting or slightly inflecting, and generally situated at junction points of adjoining zooecia; typically two to four acanthopores associated with each zooecium. Clusters of somewhat larger zooecia may represent maculae. Mesopores lacking.
• In longitudinal section of hemispherical zoarium, zooecia radiate outward and upward from center of base; in encrusting zoarium, zooecia erect throughout. Zooecial walls of essentially uniform thickness throughout zoarium, possibly somewhat thicker in outer part of colony, and showing laminae obscurely; locally wall integrate, revealing poorly defined black divisional line. Diaphragms absent or rare, usually not more than four or five per zooecium. Acanthopores locally discernible; mesopores lacking.
• Remarks.-Characteristic features of this species are the absence or small number of diaphragms and the comparatively large zooecia; most species of Cyphotrypa Ulrich & Bassler have six or seven, or more, zooecia in 2 mm. Many zooecia in the holotype lack diaphragms; in one of the paratypes, diaphragms are generally more common in the basal one-third of the zoarium where they are two or three zooecial diameters apart and tend to be developed at approximately similar levels across the zoarium. This species can be distinguished readily from late Ordovician and younger species of Cyphotrypa. C. osgoodensis differs from C. corrugata (Weller) of Helderbergian (early Devonian) age in having larger zooecia, fewer diaphragms, in lacking crenulated walls, and in having more prominently developed acanthopores; from C. polygona Bassler of the Ellis Bay Formation (Gamachian) in its more conspicuous acanthopores, distinctly fewer diaphragms, and somewhat larger zooecia; and from C. expanda Bassler of the Tonoloway Formation (Cayugan) in having more prominent acanthopores, larger zooecia, and fewer diaphragms.

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