radiolaria - rads_cat - Phormocyrtis ligulata

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Phormocyrtis ligulata

Citation: Phormocyrtis ligulata Clark & Campbell 1942

Type specimens: pl.7, figs.22, 23, 27, 28

Type repository: University of California, Museum of Paleontology, San Francisco

Family (traditional): Theoperidae

Family (modern): Pterocorythidae

Shell smooth, with maximum breadth high up on thorax, the shell as a whole generally spindle-shaped, with strong surface ribs; apical horn usually relatively short (never exceeding 0.26 and sometimes only 0.1 total length), conical in outline (not exceeding 5° except in exceptional individuals), equally bladed, with four fins, tip usually sharp, basally fused to the top of the cephalis, sometimes asymmetrical although typically vertical; cephalis conical (often about 45°, exceptionally as much as 70°), the top rounded off and merged with the base of the horn, the base distinguished by change in contour at its junction with thorax, its length hardly more than 0.1 total length, and its basal diameter perhaps 1.5 times as much as the height, its sides sometimes convex and more or less rarely asymmetrical; thorax with strongly rounded shoulder reaching a maximum diameter of 0.43 total length near 0.5 total length (being approximately 45°); below this wide level the thorax rapidly contracts (48°) to the lower margin with regularly decreasing diameter, the breadth at the lowest level, commonly about 0.4 total length (sometimes more as in Fig. 22), the lowest level of thorax marked by an internal, horizontal, narrowed, septal band; abdomen continued in contour with the thorax (48°) and squarely truncated (except, of course as torn or injured) around the aperture whose diameter is most usually about 0.24 total length; wall uniform, trim; surface of cephalis, with vertical rows of four to six small, circular pores and with strong, apically decurrent, vertical, convergent, creases or ribs separating the rows, these ribs continued basally with those of the thorax; of thorax, with a dozen to fifteen vertical rows of six or eight, round, not very large, well-spaced pores, between the rows; the ribs of the cephalis are continued in similar number as even stronger and higher creaselike ribs; of abdomen, with the same number of rows of pores, these pores about three or four in a vertical row, larger and much more irregular (or even rectangular) than those of the thorax; sometimes they are more or less fused and run together in twos and threes, otherwise the framework glassy, and the ribs die away gradually above the middle of the abdomen having been continued that far from the thorax; aperture simple, its margin often torn and ragged.

Length of shell (Fig. 28), 240µm; of horn, 60µm; of cephalis, 16-25µm; of thorax 100µm; diameter, maximum 110µm; of aperture, 50µm; of thoracic pores, 4.4µm.

Distinguishing characters: A fair suite is illustrated on Plate 8, a few shells of which are a trifle unusual in one or more characters. One specimen (Fig. 28) has a much narrowed aperture, and perhaps the most representative one is illustrated in Figure 22.
Phormocyrtis ligulata n. sp. differs from the recent, Pacific species P. costata Haeckel (1887) in less contraction of abdomen, and from P. longicornis Haeckel (1887) in shorter apical horn and longer thorax. It resembles very closely Podocyrtis fasciata n. sp. but of course is not only very much shorter (about two-thirds) but also more importantly lacks the distinct lobular feet of Podocyrtis.

References:

Clark, B. L. & Campbell, A. S. (1942a). Eocene radiolarian faunas from the Mt. Diablo area, California. Geological Society of America, Special Papers. 39: 1-112. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Phormocyrtis ligulata Clark & Campbell 1942

Phormocyrtis ligulata

References:

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