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 LXIII. 
1820. Terebratulites, Schlotheim. Petrefactenkunde auf ihr. jetz. Standpunkt, p. 282. 
1830. Porambonites, Pander. Beitr. zur 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. Tei'ebvatula, von Bdch. Ueber Terebrateln, p. 104. 
1840. Spirifer, von Buch. Beitr. zur Kennt. Gebirgsform. RussL, pp. 13, 16, pi. ii, figs. 2-7. 
1840. Tevebratula, von Eichwald. Silurian System in Estland, pp. 132, 135. 
1845. Spirifer, db Vernedil. 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. Porainbonites, d’Orbigny. Paleontologie Fi-an^aise; Terr. Cret., vol. iv, p. 345. 
1850. IsorhyncMis, King. Monogr. Permian Fossils of England, p. 112. 
1852. Porambonites, von Eichwald. Lethiea rossica, vol. i, p. 793. 
1853. Porambonites, Sharpe. Quarterly Journal Geol. Soc. London, vol. ix, p. 155. 
1854. Porambonites, Davidson. Introd. British Fossil Brachiopoda, p. 99, pi. vii, figs. 120-126. 
1869. Porambonites, Davidson. British Silurian Bi-achiopoda, p. 195, pi. xxv, figs. 16 a-d. 
1877. Porambonites, Hall and Whitfield. King’s U. S. Geol. Expl. Fortieth Parallel, p. 234, pi. i, 
fig. 16. 
1889. Porambo7iites, Noetling. Zeitschr. der deutsch. geolog. Gesellsch., vol. xxxv, p. 355, pis. xv, xvi. 
1890. Porainbonites, Gagel. Brachiop. der camb. und silur. Geschiebe im Diluv. der Provinz. Ost- und 
Westpreussen, pji. 50-52, pi. v, figs. 1-7. 
* See Beecher and Clarke, Memoirs N. Y. State Museum, vol. i. No. 1, p. 32, pi. iii, figs. 14-16 a. 1889. 
Anastrophia internascens, Niagara group. 
