BRACHIOPODA. 225 



sion of the spondylium that does not appear to be accidental. The muscular 

 impressions of this valve are frequently defined as a fourfold scar about the 

 anterior end of the spondylium ; in the pedicle-valve these impressions are 

 rarely discernible. 



It has been shown that in early age the shells of Anastrophia are normally 

 biconvex, and the brachial valve scarcely deeper than the opposite.* In this 

 condition the form of the shell resembles that of normal individuals of Cama- 

 rella Volborthi, and in this series of forms, beginning in Camarella where senile 

 shells evince a gibbosity of the brachial valve and a tendency toward reversion 

 of convexity, and ending with the Lower Helderberg Anastrophia Verneuili, we 

 have a consecutive and gradational development in internal structure, which is 

 accompanied by more abrupt variations in exterior. On the basis of the former 

 it would be difficult to apprehend where division lines should be drawn, but the 

 differences in the latter afford immediate and reliable means of distinction. 



Genus PORAMBONITES, Pander. 1830. 



PLATE LXUI. 



1820. Ter^atulites, Schlothbim. Petrefactenkunde auf ihr. jetz. Standpunkt, p. 282. 



1830. Poravibonites, Pasder. Beitr. zui- Geogn. des russ. Reiches, pp. 95-100, pi. iii, fig. 9 ; pi. xi, 



figs. 1-8 ; pi. xii, figs. 1-8 ; pi. xiii, figs. 1-7 ; pi. xiv, figs. 1-4 ; pi. xv, figs. 1-4 ; 



pi. xvi A, fig. 12 ; pi. xvi B, fig. 7. 

 1834. Terebratuia, von Buch. Ueber Terebrateln, p. 104. 



1840. Spirifer, vow Buck. Beitr. zur Kennt. Gebirgsform. Russl., pp. 13, 16, pi. ii, figs. 2-7. 

 1840. Terebratuia, ton Eichwald. Silurian System in Estland, pp. 132, 135. 

 1845. Spirifer, db Vbrnbcil. Geol. de la Russie et des Mont, de I'Oural, vol. ii, pp 127, 130-134, pi. ii, 



figs. 2, 3 ; pi. iii, fig. 1. 

 1847. Poraiabonites, d'Okbigny. PalSontologie Fransaise ; Terr. Cret., vol. iv, p. 345. 

 1850. Isorhynchm, Ki.vo. Monogr. Permian Fossils of England, p. 112. 

 1852. Poratnbonitcs, vos Eicuwald. Lethsea rossica, vol. i, p. 793. 

 1863. Porainbonites, Sharps. Quarterly Journal Geol. Soc. London, vol. ix, p. 155. 

 1854. Porambonites, Davidsok. Introd. British Fossil Brachiopoda, p. 99, pi. vii, figs. 120-126. 

 1869. Porambonites, Davidson. British Silurian Brachiopoda, p. 195, pi. xxv, figs. 16 a-d. 

 1877. Poratnbonitet, Hall and Whitkibld. King's U. S. Geol. Expl. Fortieth Parallel, p. 234, pi. i, 



fig. 16. 



1889. Pirrambonites, Nobplino. Zeilschr. der deutsch. geolog. Gesellsch., vol. xxxv, p. 355, pis. xv, xvi. 



1890. Porainbonites, Gaqbl. Brachiop. der camb. und silur. Geschiebe im Diluv. der Provinz. Ost- und 



Westpreussen, pp. 50-52, pi. v, figrs. 1-7. 



* Sea Bboohbb and Clabkb, Memoii-s N. Y. State Museum, vol. i. No. 1, p. 3i, pi. iii, figs. 14-16 a. 1889. 

 Anoftrophia internascens, Niagara group. 



