BRACHIOPODA. 307 



GEN ERA 



WHOSE SYSTEMATIC POSITION IS UNDETERMINED. 



Genus EICHWALDIA, Billings. 1858. 



PLATE LXXXni. 



1848. Terebratula, Davidson. Bull. Soi\ Geol. de France, second sei-., vol. v, pi. iii, lig-. 34. 



1849. Atrypa, d'Orbigny. Pi'odrome de Pal^ontologie, vol. i, p. 40. 



1852. Ati-ypa, Hall. Palseontolofry of New York, vol. ii, p. 281, pi. Ivii, tig-a. :>a-t. 



1858. Eichxoaldia, Billing.s. Rept. Geol. Survey Canada for 1857, p. litO, fig.s. 24 a-e. 



1859. RhynchoneUa, Po7-amhoniU's, Salter. Muvchison's Siluria, second ed., pp. 250, 544. 



1860. Poramhonltes, LindstrOm. Gotland's Brachiopoden, p. 364. 



1863. RliynclwHella- Hall. Transactions of the Albany Institute, vol, iv, p. 217. 



1866. EicJiwaUUa, Billings. Catalogue Silurian Foss. Anticosti, p. 10. 



1867. Eicliwaldia, Dictyonella, Hall. Twentieth Ann. Rept. N. Y. State Cab. Nat. Hist., pp. 274-278, 



figs. 1-7. 

 1869. Eicliwaldia? Davidson. British Silurian Brachiopoda, p. 193, pi. xxv, figs. 12-15. 

 1875. EicJiwahUa, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 159, |)1. xxvi, 



figs. 50-54. 



1879. Eichwaldia, Barrande. Systeme Silurien du Centre de la Bohriue, vol. v, pi. Ixxxi. figs. I-III. 



1880. Eichwaldvi, Lind.strom. Angelin's Fragmenta Silurica, p. 25, \\\. ii, figs. 16-20. 



1883. Eichioaldia, David.son. British Silurian Brachiopoda, Suppl., p. 140, pi. viii, tigs. 15, 16. 



1884. Eicliwaldia, David.son. British Fossil Brachiopoda, General Summary, p. 355. 

 1884. Eichioaldia, Young. Geological Magazine, vol. i, No. 5, p. 214. 



1889. Eicliwaldia, Beecher and Clarke. Mem. N. Y. State Mu-!., vol. i. No. I, p. 31, pi. iii, 

 figs. 11-13. 



These curious shells have been carefully studied by Billings, Hall, Davidson, 

 LiNUSTROM and Young, and though we have a pretty complete understanding of 

 their structure, their affinities and phylogeny are still obscure. Their charac- 

 ters are as follows : 



Shells subtriangular in outline, with biconvex valves, the pedicle-valve hav- 

 ing a broad median sinus, and the brachial valve a corresponding median fold. 



The umbo of the pedicle-valve is acute and arched over the opposite valve, 

 though not closely appressed against it. As far as has been ascertained, the 

 umbonal space between the two valves is open, that is, there is no normal delti- 

 dium or pair of deltidial plates extending from the apex downward ; but there is a 



