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- C2 Sequence (Fairview: Fairmount)
Identification in Hand Sample
- Large, convex whorls with round narrow shoulders
- Spire shorter than aperture
- Incised sutures
- Surface of shell is smooth to polished
Cyclonema limatum from the Fairview Formation of Cincinnati, Ohio (CMC 63813)
- Diagnosis. — Turbiniform shell gradational to Holopea, convex whorls with round narrow shoulders, smooth polished surface, ornament of lirae, anomphalous.
- Description. — Large inflated shell, spire shorter than aperture, sutures incised and shoulders rounded, whorls convex, body whorl large and inflated; nucleus unknown, anomphalous; aperture ovate and auriform, outer lip rounded above and below, straight at widest expanse, extending onto body whorl at upper suture; columellar lip thin, irregular, slightly reilexed, not excavated, usually oblique inward toward aperture; surface of shell is smooth to polished, ornamented by closely spaced delicate collabral lirae which extend obliquely across body whorl, often forming small growth wrinkles at aperture, well-preserved specimens show faint spiral threads which become stronger on base of mature body whorl, ornament may extend onto penultimate whorl.
- With the exceptions of C. limatum and C. transversum which lack spiral ornament, cords are always present even if other spiral ornament is absent.
- Weakly ornamented species of Cyclonema appear to be related to Holopea as evidenced by C. limatum. Holopea has a smooth, polished surface ornamented only by collabral growth lirae. C. limatum Ulrich is similar but well-preserved specimens show faint spiral threads on the base of mature whorls. The ornament of C. limatum is identical to that of C. sublaeve Ulrich and closely resembles that of C. gracile. The shape of C. limatum is less convex and inflated than Holopea and, again, resembles C. sublaeve.
- As far as known, C. limatum is the only species bearing a parietal inductura and it is poorly developed compared to that of Naticonema.
Ulrich & Scofield (1897):
- Shell 25 to 30 mm. in height, the greatest width generally about a fifth less, consisting, without the nucleus which is unknown, of about four rapidly enlarging ventricose whorls; suture distinctly impressed though not deeper than necessitated by the uniform convexity of the whorls; aperture large, higher than wide, rounded below, somewhat acuminate ovate in outline; inner lip nearly straight, not as thick as usual in Cyclonema, while as a rule it is merely flattened instead of excavated, and turned inward so that the flat portion is not fully visible in a ventral view; surface smooth, sometimes polished, the lines of growth obscure; of revolving lines not a trace is to be seen except on two specimens where the surface is glossy as though they retained patches of epidermis that is generally not preserved. In its general aspect this fine species reminds one strongly of Holopea, and it is possible that it would be more naturally placed in that genus. It has seemed to us, however, that the characters of the inner lip, which is sometimes excavated as in Cyclonema, would not permit its reference to Holopea, in which, as the genus is now understood, the inner lip is thin and simple. Perhaps C. limatum indicates a partial reversion to ancestral characters – in other words, a form in which larval characters are retained through adult stages.