BRACHIOPODA. 225 



sion of the spondylium that does not appear to l)c accidental. The muscular 

 impressions of tliis 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 Anastropiiia 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, wliich 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. TerebratuHtes, Schlotheim. Petrefactenkunde auf ihr. jetz. Stan(ipiinkt, p. 282. 



1830. Poi-amh(mU(S, Pahder. Beitr. zui- Geogn. des riiss. Reii'hes, 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. xviB, tig. 7. 

 1834. Terehrattda, vos Bvcn. Ueber Terebratein, p. 104. 



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

 1840. Tenhratula, von Eichwald. Silurian System in Estland, pp. 132, 135. 

 1845. iSpirlfei; de Vernedil. Geol. de la Russie et des Mont, de I'Oiiral, vol. ii, pp 127, 130-134, pi. ii, 



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

 1847. Pvi-ambonites, d'Okeignt. Paleontologie Fran^aise ; Tei-r. Cret., vol. iv, p. 345. 

 1850. Isorhynchafi, Kl.VG. Monogr. Pei-mian Fossils of England, p. 112. 



1852. Purambonilcs, von Eichwald. Lethiea rossica, vol. i, p. 793. 



1853. Poramhonites, Sharpe. Quarterly Journal Geol. Soc. London, vol. ix, p. 155. 



1854. Porambojiites, Davidson. Introd. Bi-itish Fossil Brachiopoda, p. 99, pi. vii, figs. 120-126. 

 1869. Porambonitcs, Davidson. British Silurian Brachiopoda, p. 195, pi. xxv, figs. 16a-rf. 



1877. Parambonites, Hall and Whitfield. King's U. 8. Geol. Exjil. Fortieth Parallel, p. 234, pi. i, 

 fig. IB. 



1889. Pwambonites, Noetling. Zeilschr. der deutsch. geolog. Gesellsch., vol. xxxv, p. 355, pis. xv, xvi. 



1890. Porambouites, Gagel. Bnichioii. dei- camb. uud silur. Geschiebe im Dihiv. der Provinz. Ost- and 



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



* See Bebcher and Clarke, Memoirs N. Y. State Museum, vol. i. No. 1, p. 32, pi. iii, figs. 14-16 a. 1889. 

 AnoDtrophia intei'nasceiis, Niagara group. 



