. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. Fig. 23. Pseudocalycoceras angolaense (Spath). The holotype (after Douville 1931). x 1. whorl section is slightly compressed, almost quadrate, with a polygonal costal section. On the outer whorl of SAM-PCA2731, about 18 ribs are weakly developed on the umbilical wall and pass radially to the umbilical shoulder where they give rise to 1-2 flank ribs. The umbilical tubercles are irregularly developed, and there are only 12 on the outer whorl. The flank ribs are flexuous, rursiradiate, and number about
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. Fig. 23. Pseudocalycoceras angolaense (Spath). The holotype (after Douville 1931). x 1. whorl section is slightly compressed, almost quadrate, with a polygonal costal section. On the outer whorl of SAM-PCA2731, about 18 ribs are weakly developed on the umbilical wall and pass radially to the umbilical shoulder where they give rise to 1-2 flank ribs. The umbilical tubercles are irregularly developed, and there are only 12 on the outer whorl. The flank ribs are flexuous, rursiradiate, and number about 30 on the outer whorl. At the prominent lower ventro-lateral clavi the ribs flex forwards to the upper ventro-lateral clavi and then cross the venter transversely. All ribs bear prominent siphonal clavi. The penultimate whorl of this specimen is very weakly ornamented and shows the earliest whorls to have lacked ribbing, at least on the lower portion of the flanks, and umbilical tubercles to a diameter of about 20 mm. Together with the above specimen, three other examples, SAM-PCA2767, SAM-PCA2777 and SAM-PCA2772, provide an almost complete ontogenetic sequence for this species. In SAM-PC All 61 (Fig. 4J-K) the flanks are entirely smooth to a diameter of 11 mm, at which stage, in SAM-PCA2777 (Fig. 4A-C), ventral tuberculation appears, as well as very faint ventral ribbing. By 15 mm diameter the ribbing has become more prominent, but is still confined to the outer flanks, while the umbilical shoulder bears occasional weak umbilical tubercles. At this stage the whorl section is oval, with slightly convex flanks con- verging to the narrowly arched venter. In costal section the venter is almost tabulate and trituberculate. In this same specimen the lower ventro-lateral. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original w
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
