Placenticeras kaffrarium Morph kaffrarium Etheridge

Microconch. The shell is tumid (WB/H = c. 0.95) with a broad clavate venter. The shell is strongly evolute (U/D = 0.32-0.47; Av. = 0.38; S.D. = 0.05), the flanks are flattened to weakly curved in the early stage, and may become strongly convex on the adult body chamber. Some compressed specimens exhibit a trigonal whorl section in the early stage, then become subtrigonal, and, finally, polygonal in the adult body chamber. However, in some inflated forms, the whorl section ranges from subtrigonal to polygonal. In highly ornate forms, robust ornament appears at an early stage. Ribs are prominent; primaries are short and bifurcate near the umbilical tubercles; secondaries are straight to slightly flexuous and terminate at the ventrolateral tubercles, which are nodose to bullate. The peristome has a ventral rostrum. The diameter may be up to 138 mm (Range = 72-138; Av. = 89; S.D. = 21.44).

Macroconch. The shell is similar to that of the microconch in the inner whorls, but shows variation in the adult whorls with respect to diameter, degree of involution, and strength of ornament. Maximum diameter may be up to 186 mm (Range = 90-186; Av. = 130.29; S.D. = 23.27). The venter is strongly clavate; this persists up to a variable length on the adult body chamber, which finally becomes smooth and rounded. Shell tumidity (WB/ H = c. 1.02) and degree of involution (U/D = 0.29-0.47; Av. = 0.38; S.D. = 0.027) are less than those in the microconch. Again, there is covariation between inflated, evolute shells and the strength of the orn amentation. The strength of the lateral tubercles increases up to the first quarter of the adult body chamber; afterwards, they persist with attenuated strength. In the early to middle phragmocone stage, the umbilical tubercles are spinose, and more robust than the lateral tubercles, but, in the late phragmocone stage to the early part of the mature body chamber, the lateral tubercles appear to be stronger than the umbilical tubercles. The shell becomes smooth with a rounded venter near the aperture. The peristome is simple.

Fig. 5.6 Subkaffrarium type of ornament. 1, lateral view, macroconch, incomplete body chamber. 2, lateral view, macroconch, adult phragmocone; note part of the body whorl preserved 3, ventral view, macroconch; note weakly developed clavi. 4, lateral view, macroconch, adult with major part of the body chamber preserved; note strength of umbilical tubercles decreases towards the aperture. Scale bar = 1 cm.

Fig. 5.6 Subkaffrarium type of ornament. 1, lateral view, macroconch, incomplete body chamber. 2, lateral view, macroconch, adult phragmocone; note part of the body whorl preserved 3, ventral view, macroconch; note weakly developed clavi. 4, lateral view, macroconch, adult with major part of the body chamber preserved; note strength of umbilical tubercles decreases towards the aperture. Scale bar = 1 cm.

Was this article helpful?

0 0

Post a comment