Ambocœlia Hall and certain Similar British Spiriferidæ

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Abstract
Several small Spirifers of the Upper Palæozoic rocks of this country have been referred to Ambocœlia Hall. This genus was proposed to include certain American Devonian and Carboniferous forms with a peculiar internal structure; the genotype, designated by Hall, is Orthis umbonata Conrad, a species from the Hamilton Group (Lower Devonian) of North America. In the paper in which he established the genus, Hall (1860, p. 71) suggested that Spirifer unguiculus Sowerby sp. (a British Devonian form) might also be included in the genus. The opinion generally held, for example by King (1850, p. 135) and Davidson (1858, vol. ii, pt. 4, p. 59), that Spirifer unguiculus is closely allied to, if not identical with, Spirifer urei Fleming and Martinia clannyana King, led observers to place these species also in the genus Ambocœlia . It naturally followed that, so far as the British species were concerned, the genus was described in terms of the external form of these species. In particular, emphasis was laid upon the presence of a dorsal valve considerably flatter than the ventral, and upon the development of a more or less narrowly defined median sulcus in the former. Such a procedure resulted in a neglect of the internal features that Hall so clearly distinguished. Further, the discovery of spines in Martinia clannyana , and later in Spirifer urei , led to a belief that a spinose surface is also characteristic of the genus. In no instance, so far as I am aware, has any reference been made to the

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