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Published online by Cambridge University Press: 01 May 2009
Many beds of limestone, belonging to the middle division of the Upper Silurian formation of the Island of Gotland, consist almost entirely of the fragments of a very large and peculiarly-shaped Brachiopodous shell. It may be regarded as one of most characteristic fossils of these Upper Silurian rocks. Perfect valves, giving a satisfactory view of its structure have never been found. When Mr. Davidson, with his usual kindness, sent me copies of the figures and descriptions given by Mr. Billings, of the new genus Trimerella, found in Canada, I had no hesitation in referring both the Canadian and the Gothlandic shells to the same genus. The materials obtained by Mr. Billings seem to have been more incomplete than mine; I have, therefore, been able to make some additions to the description given by him.
Translated and communicated by the Author from the “Ofversigt af Kongl Vetenskaps-Akademiens Förhandlingar,” 1867. No. 5. pp. 253–257.
page 441 note 2 Billings, , Geol. Survey of Canada, Pal. Foss., Vol. I., p. 167.Google Scholar
page 442 note 1 Davidson, , Silurian Brachiopoda, pl. ii, fig. 35; pl. iii., figs. 5, 6.Google Scholar
page 442 note 2 Davidson, (1. c. pl. iv, fig. 39). Compare also fig. 4 of my plate with the figure of a dorsal valve of Trimerella grandis in the work of Mr.Billings, .Google Scholar
My above stated opinion as to the nature of the siphons of Trimerella is corroborated by the fact that in some species of Crania, especially the Cretaceous, these scars of the adductors continue in the form of narrow pointed siphons, ceasing at the apex of the valves. Thus, for instance, in Crania spinulosa, Hisinger, Leth. Suecica, pl. xxiv., fig. 7a; also, C. Brattenburgensis, in the German edition of Davidson's “Introduction to the Brachiopoda,” pl. v, fig. 15 and C. antiqua, Defr., pl. v, fig. 16c. I can also cite the valuable authority of the late Dr.Woodward, S. P., in his “Manual of the Mollusca,” p.236. (Crania), “The large muscular impressions are … sometimes deeply excavated.”Google Scholar