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Genotype: Fusus ferrieri Philippi.
The value and systematic position of this genus are by no means established. It was placed in this family because of the strong spirals on the base, thus resembling the South American members. Cossmann rightly considered the creation of the genus on the material available “premature,” as the aperture was unknown. The excellent figure (Wilckens, 1904, pl. 18, fig. 5), however, shows that the course of the growth-lines of the outer lip is the same as that of Belophos, which has many Tertiary representatives in New Zealand. Other features of agreement are the concave shoulder, with fine spirals, much stronger spirals below, and the presence of axial sculpture. A figure of the New Zealand Belophos
Fig. 1.—a. Struthiolariopsis ferrieri (Phil.). (After Wilckens.)
b. Belophos sulcata (Hutton).
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cf. sulcata (Hutton) is given (text-fig. 1b) for comparison with the type of Struthiolariopsis. The chief differences observable are the longer axials and the higher whorls of the former.
Another species attributed to this genus is Struthiolariopsis similis Wilckens (1922, p. 17), from the Upper Senonian of Amuri Bluff, New Zealand; but unfortunately this shell does not in any way improve the position. Wilckens was not sure whether there was an anterior canal, but the aperture of the type and only specimen has now to some extent been cleared of the hard matrix (see text-fig. 2). The columella is quite straight, and, where broken, the canal shows little taper, so it was originally much longer. This, with the strong biangulation of the body-whorl, the nodules on the shoulder-angle, the course of the growth-lines, and the disposition of the spiral ornamentation, indicates generic, perhaps even specific, agreement with Tudicula alta Wilckens, figured by him on the same plate, and occurring at the same locality.
Fig. 2. “Struthiolariopsis” similis Wilckens (holotype).
Struthiolariopsis should therefore be removed from the Struthiolariidae and put near Belophos. The latter genus was placed by Cossmann (1901, p. 37) in the Buccinidae, but its shape, aperture, and ornamentation show relations with Pseudotoma, the only difference being the deeper anterior notch of the canal.
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The shells hitherto classed under Struthiolaria sensu lato present a considerable diversity of appearance, and several well-defined divisions can be made:—
| 1. |
Monalaria n. g. Outer lip with broad sinus above sweeping round to a convex wing below, columella straight.
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| 2. |
Struthiolarella Steinmann and Wilckens. Outer lip as in 1, columella slightly bent in youth, curvature increasing with age; whorls subangled, early sculpture of curved axials, later abbreviated to rounded tubercles, fine spirals above, strong cinguli below. Ex. S. ameghinoi von Ihering. |
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| 3. |
Struthiolaria Lamarck. Outer lip bisinuous, columella bent well to right.
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| 4. |
Tylospira Harris. Outer lip bisinuous, columella well bent, lightly calloused at an early stage, but continuing to grow forward so that no sculpture is formed on the body-whorl. Ex. B. scutulatum Martyn. |
The four main divisions, based on the formation of the aperture, are here given generic rank, and that these genera have sprung from a common stock appears on a study of their ornamentation.
Grabau (1902) was the first to apply the theory of recapitulation to the development of gasteropod sculpture, notably for Fusus (1904). Additional groups have been worked out by Miss McDonald, Dr. Trueman (1921), and others.
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The following is an attempt to discover the phylogeny of the family by following the ontogeny of some characteristic species.
Well-preserved examples of the Recent and Pliocene S. papulosa and S. vermis show, in most cases, a small almost planorbid apex of one or two smooth volutions. This has always been considered as the protoconch; but a surprising condition was revealed by some specimens of S. vermis from the Wanganuian Pliocene. In these the protoconch is a smooth, bulbous, capuliform structure, with its long axis at right angles to that of the shell (a particularly large and projecting example is figured in text-fig. 3, a–c). That this is the true protoconch is shown by the
Fig. 3—Protoconch of Struthiolaria vermis. × 6.
appearance of the same feature on specimens of S. convexa n. sp. from the Pliocene of the Ngaruroro River. In withdrawing from the embryonic shell the animal constructs numerous septa, so that, the hollow bulb being easily broken off, a planorbid apex is the result. It is probable that this type of protoconch prevails throughout the genus, for the smooth planorbid tip, generally seen in all well-preserved shells, is followed by a convex, striated conch-whorl similar to that following the deviated protoconch of the examples cited above.