Letter | Published:

Shell-structure of the Brachiopod Lacazella mediterraneum (Risso)

Naturevolume 175pages11231124 (1955) | Download Citation

Subjects

Abstract

THE continued use of Beecher's ordinal classification1 of the Brachiopoda despite its inconsistencies2 is mainly due to his fascinating interpretation of Kovalevskii's observations3 on the development of the recent thecideid Lacazella. Beecher concluded that the pseudodeltidium was secreted not by the mantle fold of the thoracic segment but by the caudal segment, and that only later was it ankylosed to the pedicle valve. Further, the pseudodeltidium appeared to be identical with a similar structure invariably found in the extinct strophomenoids (the central group of his order Protremata), a comparison that led him to regard the thecideids as derivatives of that stock. In other articulate brachiopods (the Telotremata of Beecher), the delthyrium is usually constricted by deltidial plates, sometimes fused into a single unit, which are undoubtedly secreted by extensions of the mantle. Thus on the assumption that the pseudodeltidium was a ‘third shell’, Beecher was able to draw a fundamental distinction between the two groups. Substance was added to the supposed alien nature of the pseudodeltidium by his belief that in protrematous brachiopods the pseudodeltidium was always impunctate, even when the valves were punctate as in the strophomenoids.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1

    Beecher, C. E., Amer. J. Sci., Ser. 3, 44 (1892).

  2. 2

    Cooper, G. A., “Index Fossils of North America” (Wiley, 1944). Arber, M. A., Geol. Mag., 77 (1940).

  3. 3

    Kovalevskii, A. O., Izvyest. Imp. Obshch. Lyub. Estest. Antrop. Étno., 14 (1874).

  4. 4

    Kozlowski, R., Paleont. Polonica, 1 (1929).

  5. 5

    Elliott, G. F., Ann. Mag. Nat. Hist., Ser. 12, 6, 693 (1953).

Download references

Author information

Affiliations

  1. Geology Department, The Queen's University, Belfast

    • ALWYN WILLIAMS

Authors

  1. Search for ALWYN WILLIAMS in:

About this article

Publication history

Issue Date

DOI

https://doi.org/10.1038/1751123a0

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.