^{page 13 note 1} Eichwald, , Zoologia Specialis, vol. i. p. 274, 1829.Google Scholar Von Buch, Beiträge zur Bestimmung des Gebirgsformation Russlands, 1840. Kutorga, Ueber die Siphonotreteæ, 1848. De, Verneuil, Geol. of Russia, vol. ii. 1845.Google ScholarDavidson, , British Fossil Brachiopoda, vol. i., Introduction, p. 131, 1853,Google Scholar and vol. iii. Sil. Mon. p. 75.

^{page 13 note 2} Morris, , Annals and Mag. Nat. Hist. vol. iv. No. 23, p. 315, 11. 1849.Google Scholar

^{page 13 note 3} M'Coy, , Annals and Mag. Nat. Hist. vol. viii. p. 389, 1851.Google Scholar

^{page 14 note 1} Prof. W. King has kindly favoured me with the following remarks he had made on the shell and spines of one of the Russian species:—“The valve of Siphonotreta, as stated by Kutorga, consists of a dermis of a horny nature, an inner perlaceous layer, and an intermediate one of considerable thickness, and containing calcareous matter. Probably an analysis would determine the presence of phosphate of lime in the valves, as in those of Lingula and Discina. The dermal layer, the only one that could be tried, slightly effervesces on the application of acid: the same test, however, discloses abundance of lime in the casts of the fossils. Morris has noticed that the valves have a distinctly ‘perforated structure’; also that their outer surface is ornamented with numerous tubular spines, generally arranged in a very regular order, leaving, when broken off, slightly projecting hollow tubercules in their place. He does not mention that the spines are continuous with the perforations; but it may be inferred that this peculiarity was not unsuspected by him. The spines in the specimens of Siphonotreta unguiculata under observation are only preserved on portions of the valves near their margin; elsewhere their presence is indicated by minute tubercules or pimples. It was these that led De Verneuil to characterize the shell ‘a surface chagrinée’ Between the pimples the surface is marked with fine raised reticulating lines. The tubularity of the spines is indicated by an opaque medial line in the midst of their subtranslucent substance (Fig. A.). The spines, when transversely truncated, exhibit very clearly the position of their contained tube; besides, the pimples frequently show a hollow, corresponding to the tube, in their centre. The inner surface of the valve is marked with regular cup-shaped depressions (eminences on a cast of it), containing in their centre a minute deep cavity (Fig. B.); which is doubtless continued through the thickness of the valve into the tube of the external spines, but the connexion is not satisfactorily exhibited, evidently through molecular changes which the intermediate layer of the valves has undergone. From the preceding remarks it will be seen that the spinose peculiarities of Siphonotreta unguiculata, instead of being simply dermal processes, as is the case in Discina, are of the nature of those known to characterize Productus, Strophalosia, Rh. spinosa, and some other Palliobranchs. Whether the tubularity of the spines in Siphonotreta and the fossils just named, is homologous to the perforated shell structure common to Terebratula, Spiriferina, and other genera of their class, is a question which does not seem to be sufficiently advanced for determination at present. Often the hollows on the inner surface of the valve contain a dark-coloured infilling; and frequently they are charged with a greenish subtranslucent mineral substance, which certain Canadian Eozoonites, unnecessarily anxious to meet with a case of the kind, would probably regard as serpentine; but without denying the possibility of such a methylised product occurring as a fossil infilling, the substance in question seems more likely to be one of the numerous varieties of glauconite; or possibly, it may be related to apatite, and derived from the phosphate of lime of which the shell structure of Siphonotreta was to some extent originally composed. The hollows in the pimples, on the outer surface, are also often filled with the same substance; which fact may be offered as further supporting the conclusion that there is a tubular connexion between the inner and the outer surface of the valves.”