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- C1 Sequence (Clays Ferry/Kope: Economy/Fulton)
Identification in Hand Sample
- Slender, narrow cup and nonpinnulate arms that branch isotomously
- Brachials are prominent at the superior lateral angle
- Simple armlets about half as stout as the main arm from which they spring
- Has a small, solid, discoidal holdfast
Merocrinus curtus from the Eden Formation of Carrollton, Kentucky (OUIP 111 and OUIP 5)
- A species of Merocrinus with smooth aboral cup and arm plates. Cup cylindrical with relatively wide base; radials fully in contact, with wide radial facets; infrabasals high and radials short compared to cup height. Arms with relatively wide brachs, especially the proximal ones, compared to most merocrinids; arms with bilateral heterotomy above the primibrachs; highest observed axillary located on quartibrachs; arms with at least eight branches per ray; roughly average numbers of brachs in various parts of arms for genus. Anal sac straight, at least up to proximal tertibrachs.
- However, a single specimen from the lower Kope, Fulton submember, which is the only source for Merocrinus curtus Ulrich, 1879, has a small, solid, discoidal holdfast cemented to a bryozoan with an intact distal column resembling that of Merocrinus (Fig. 2.9). This single specimen suggests permanent, cemented attachment in M. curtus. Surprisingly, few such holdfasts have been notes in associated with Merocrinus columns; possibly some have been identified as Anomalocrinus Meek and Worthen, 1865.
Meyer et al. (2002):
- Cladid with a slender, narrow cup and nonpinnulate arms that branch isotomously (Moore and Teichert, 1978, Fig. 409)/ Cup width does not greatly exceed that of the stalk. Total stalk length is unknown, although a stalk measuring more than 60 cm without crown or termination was found in the lower Kope Formation at Duck Creek near the k445 section.
- All known species of Iocrinus further resemble one another in the marked incrication of the brachials; while the species of Merocrinus have as a simple rule smooth brachials, although M. curtus, as figured and described by Ulrich (“Dendocrinus curtus,” Journ. Cincinnati Soc. Nat. Hist., II, p. 18 pl. vii, fig. 14, 1879), has brachials “prominent at the superior lateral angle.” The very slight development of this feature in the Mincop specimen is therefore characteristic of Merocrinus rather than of Iocrinus.
- From Merocrinus curtus specimen A is clearly distinguished by the regular dichotomy of its arms, for in M. curtus there are simple armlets, “about half as stout as the main arm from which they spring.” The cup is also lower in M. curtus.