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Alvarez, F. & Brunton, C. H. C. 1990 04 15: The shell-structure, growth and functional morphology of some Lower Devonian athyrids from northwest Spain. Lethaia, Vol. 23, pp. 117–131. Oslo. ISSN 0024–1164.

In the Emsian (Lower Devonian) of northwest Spain three congeneric species of athyrids have been recognized principally by their, as yet, unique shell microstructures. The shell remains thin throughout ontogeny, with hardly any internal thickening, while the external lamellac are long and two to four times as thick as the valves. being composed of many layers of secondary fibres. A growth model for these shells is presented, including the recognition and differentiation of true valve growth as compared to growth of lamellae. Functional morphology is discussed and a new explanation presented for the function of the visceral foramen. The possible growth and disposition of the lophophore are described and, taken together with morphological and environmental factors, an anterior inhalant water circulation system is proposed. *Brachiopods, Athyrididae, Devonian, shell-structure, growth. functional morphology.