Other formats

    TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

The Atoll of Funafuti, Ellice group : its zoology, botany, ethnology and general structure based on collections made by Charles Hedley of the Australian Museum, Sydney, N.S.W.

[introduction]

A member of the Mangiliinæ, distinguished by three stout tubercles seated on the lip within the aperture, and by a globose, tilted, two-whorled protoconch, which is closely spirally grooved throughout.

The new species, which typifies this proposed new genus, stands apart from almost all Pleurotomidee, with regard to the few large denticules which defend the aperture. The thickened lip and anal notch throw it into Tryon's subfamily Mangiliinæ, and among the members of that, Glyphostoma makes the nearest approach. Glyphostoma has smaller and more numerous denticules, and an apex which in G. gabbii is thus described by Dall:—?" nucleus acute, three-whorled, the first whorl smooth, rounded, tilted, minute; the others smooth, polished, keeled on the periphery." This description fits others I have examined such as G. malleti. In various instances the protoconch of Mangelia is shown by Watson to have delicate, longitudinal ribbing. The genus Glathurella has a peculiar raised mesh-work over all the whorls of the protoconch, as here illustrated in the case of C. irretita, and which has been beautifully figured in several instances by Watson in the " Challenger" Report. The apex which Cossman gives as characteristic of Clathurella is, however, quite different.§

Opinions on the systematic importance of the Pleurotomoid protoconch are conflicting. Watson remarks that:—" sculpture and form of apex may probably serve as the safest basis of classification in the whole group." On the contrary Dall has expressed his opinion that:—"so far as our knowledge goes, nuclear page 473characters have little absolute systematic value in this group, and their relative value remains to be determined."*

Even should little weight attach to the nuclear distinction of Thetidos, the aperture, so curiously imitating Sistrum or Pupa, may separate it from its kindred, only excepting Clathurella idiomorpha, Hervier, and Clathurella rugosa, Mighels. As those authors paid no special attention to the protoconch, I am unable to decide whether they should also enter my genus.

I have no information relative to the presence or absence of the operculum, since to obtain such would entail the destruction of the only shell. It may be that in this family the thickening of the lip, followed by the development of the labial teeth, and consequent narrowing of the aperture has accompanied the degeneration of the operculum. The safety of the animal being thus secured by the exchange of one defence for another.

Dall—Loc. cit., p. 109.

§ Cossman—Essais de Palèoconchologie cornparèe, ii., 1896, p. 122.

Watson—Chall. Rep. ZooL, xv., 1886, p. 361.

* Dall—Loc. cit., p. 75.

Hervier—Journ. de Conch., xliv., 1896 (1897), p. 147; xlv., 1897, p. 110, pl. iii., fig. 3.

Langkavel—Donum Bismarckianum, 1871, p. 2, pl. i., fig. 5.