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Type species: Homotrypa curvata (Ulrich, 1882)
Species in Cincinnatian of Ohio, Indiana, Kentucky (Bryozoa.net)

  • Homotrypa curvata (Ulrich, 1882)
  • Homotrypa alta (Cumings and Galloway, 1915)
  • Homotrypa cincinnatiensis (Bassler, 1903 )
  • Homotrypa communis (Bassler, 1903 )
  • Homotrypa cf. H. creditensis (Dyer, 1925)
  • Homotrypa cressmani (Karklins, 1984)
  • Homotrypa cylindrica (Bassler, 1903)
  • Homotrypa dawsoni (Nicholson, 1881)
  • Homotrypa dumosa (Bassler, 1903)
  • Homotrypa flabellaris (Ulrich, 1890)
  • Homotrypa glabra (Cumings and Galloway)
  • Homotrypa grandis (Bassler, 1903)
  • Homotrypa libana (Bassler, 1903)
  • Homotrypa nicklesi (Bassler, 1903)
  • Homotrypa nodulosa (Bassler, 1903 )
  • Homotrypa norwoodi
  • Homotrypa obliqua (Ulrich, 1882)
  • Homotrypa pulchra (Bassler, 1903)
  • Homotrypa ramulosa (Bassler, 1903)
  • Homotrypa richmondensis (Bassler, 1903)
  • Homotrypa wortheni (James, 1882)

Taxonomic History (Nickles & Bassler, 1900)

  • 1882 Homotrypa Ulrich, Jour. Cincinnati Soc. Nat. Hist., V, p. 240.
  • 1883 Homotrypa Foord, Contr. Micro-Pal. Cambro-Sil., p. 9.
  • 1889 Homotrypa Miller, North American Geol. Pal., p. 309.
  • 1890 Homotrypa Ulrich, Geol. Sur. Illinois, VIII, pp. 370, 409.
  • 1893 Homotrypa Ulrich, Geol. Minnesota, III, p. 235.
  • 1896 Homotrypa Ulrich, Zittel’s Textb. Pal., (Engl. ed.), p. 273.
  • 1897 Homotrypa Simpson, Fourteenth Ann. Rep. State Geologist New York for the year 1894, p. 575.

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Geologic Range
Late Ordovician

Stratigraphic Occurrences


Geographic Occurrences

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Sequences (Formations)

  • C6 Sequence (Upper Whitewater, Elkhorn)
  • C5 Sequence (Saluda, Lower Whitewater, Liberty, Waynesville)
  • C4 Sequence (Arnheim)
  • C3 Sequence (Mt. Auburn, Corryville)
  • C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
  • C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

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Identification in Hand Sample:

  • Zoarium Morphology: Ramose to frondose
  • Zoecia: Often oblique; polygonal/subpolygonal; thin walled (sometimes crenulated); acanthopores usually present
  • Mesozooids: Few, generally clustered
  • Monticules: Present, often prominent, sharp-conical
  • Maculae: Larger cell apertures
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Holland (UGA Strat Lab, 2013):

  • Homotrypa is a ramose to frondose form characterized by cystiphragms, which typically form overlapping series, such as in H. alta, H. cincinnatiensis, H. curvata, H. flabellaris, H. grandis, H. obliqua, H. pulchra, H. ramulosa, H. richmondensis, and H. wortheni. In several species, the cystiphragms are isolated and form incomplete hooks, including H. austini, H. communis, H. cylindrica, H. dawsoni, H. libana, H. wortheni, H. nodulosa, and H. richmondensis. Of these, H. austini, H. communis, H. nodulosa, and H. richmondensis typically lack diaphragms and have considerably more incomplete than complete cystiphragms, suggesting to Utgaard and Perry (1964) that they might be better placed in the genus Gortanipora, which possesses only incomplete hooklike cystiphragms.

Karklins (1984):

  • The two species of Homotrypa described here, H. similis Foord and H. cressmani n. sp., conform closely to the emended diagnosis for the genus Homotrypa made by Ross (1970a, p. 373) that is followed here. Both species have autozooecia that are polygonal or subpolygonal in cross section in exozones and cystiphragms in exozones; H. similis has cystiphragms in outer endozones (subperipheral region of Ross, 1970a). The basal autozooecial diaphragms are present in the endozones of both species, but they vary in distribution. Styles (acanthopores of Ross, 1970a) are scattered and mesozooecia are sparse in both species.

Bassler (1911):

  • Numerous typical species of this interesting genus occur in the faunas of late Trenton and of Cincinnatian ages, believed to have been derived from the south Atlantic. The northern Atlantic or Arctic types occur chiefly in the Black River and earliest Trenton formations, and in America are known mainly from deposits in Minnesota and the neighboring States. Of these latter species, Homotrypa subramosa Ulrich and H. similis Foord are the most abundant and widespread species in America, and their geographic range has now been extended to the Baltic region by the discovery of specimens in several of the Russian formations. Each if these two species is quite unlike the Cincinnatian type of the genus and may be taken as typical of a variation toward Eridotrypa, while the acanthopores and the cystiphragms of H. subramosa recall Monticulipora.
  • The zoarium in Homotrypa is of ramose or frondescent, smooth or monticulated branches made up of polygonal zooecia with thin, finely crenulated walls and few diaphragms in the axial region, and thicker walls lined by cystiphragms in the peripheral zone. Mesopores are either absent or are restricted to the maculae, but acnathopores are generally present. The ramose forms of Monticulipora have great similarity to Homotrypa externally, but a thin section of the former shows a granulose wall structure very different from the clearer, more distinct walls of Homotrypa.
  • Genotype.—Homotrypa curvata Ulrich. Upper Ordovician (Maysville), Ohio Valley.

Nickles & Bassler (1900):

  • Homotrypa Ulrich: Zoarium frondescent or ramose; maculae or monticules of larger cell apertures a characteristic feature; apertures often oblique; zooecia with very thin or finely crenulated walls and remote diaphragms in immature region and cystiphragms, isolated or in series, confined to mature region; mesopores few, in clusters; acanthopores generally developed

Foord (1883):

  • External Characters: Zoarium ramose to subfrondescent; surface smooth, or with more or less prominent monticules. Cells circular, ovate or polygonal, with moderately thin walls. At intervals, there are groups of larger sized cells, which again sometimes enclose small stellate maculae, consisting of much smaller, angular cells. The surface extensions of spiniform tubuli may often be observed at the angles of the cells.
  • Internal Characters: In the axial portion of the branches or fronds, the tubes are “immature”, and may be crossed by straight diaphragms; usually diaphragms are entirely wanting in this region. The tube walls are excessively thin until they reach the peripheral regions when they are much thickened, and bend outward to open at the surface. In the peripheral or “mature” portion of the zoarium, the tubes are provided with a series of cystoid diaphragms; the space intervening between their flexuous inner line and the opposite wall of a tube is crossed by equally numerous straight diaphragms. The tube walls are perforated by rather large connecting foramina. In the tuberculated species the spiniform tubuli are numerous, but very small, and not easily recognized, while in the smooth forms they are much larger, and constitute a conspicuous feature in sections. The internal structure of the small tubes, which form the maculae of some species, is not remarkably different from that of the ordinary tubes. The only difference that I have been able to detect is found in the fact that cystoid diaphragms are but rarely developed in them.

Note: For extensive description of this genus and all associated species, see Bassler, 1903. (Specifically see page 573 for a comparative chart of species)
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H. bassleri

H. cincinnatiensis

H. dawsoni

H. flabellaris

H. hospitalis

H. norwoodi

H. obliqua

H. wortheni