BRACHIOPODA. 285 



1871. StropJtomena, Katseb. Zeitschrift (ier (ioutsch. g:eolog. Gesellschaft, vol. xxiii, jip. (520,621,624, 



62.'), 627. 630, i)l. xiv, figs. 4, 5. 



1872. Strophmneim, Barrande. Systeme Siluiien dii Centre de la Bohfme, pi. xl, fig:*. 10-19 ; pi. xlii, 



figs. 6-14, 21-28 ; pi. xliii, tigs. 1-5, 17-29 ; pi. xliv, figs. 1-30. 



1873. Strophodmita, Hall ami Whitfield. Twentv-tbinl Kept. N. Y. State Cab. Nat. Hist., pp. 236, 



239, pi. xi, figs. S-11. 



1873. StropJiodoiita, Nicholson. Rapt. Palaeontology Province of Ontario, pp. 64, 65, 67. 



1874. Strophomena, Billings. PalpEozoic Fossils, vol. ii, jip. 20, 24, 26-2!i. 



1877. Strophodonia, Hall .ami Whitfield. King's Expl. and Siirv. Fortieth P.arallel, vol. iv, p. 246, 



pi. iii, figs. 1-3. 



1878. Strophodonta, Calvin. Bulletin No. 3, United States Geological Survey, vol. iv, jip. 727, 728. 



1875. Strophodonta, Barrett. American Journal of Science vol. xv, p. 372. 



1879. Strophodonta. Hall. Twenty-eighth Rept. N.Y. State Mtis. Nat. Hist., p. 151, pi. xxiii, figs. 9, 10. 



1880. Strophomena, Dawson. Canadian Naturalist and Geologist, 2nd Ser.. vol. ix, p. 341. 



1881. Strophodonta, White. Tenth Rept. Indiana State Geologist, p. 132, pi. iv, figs. 6, 7. 



1881. Strophomena, Davidson. Brachiopoda Bndleigh-Salferton Pebble-bed, pp. 348-351, pi. xxxix, 



figs. 1, 2, 4-11. 



1882. Strophodonta, Hall. Eleventh Ann. Rept. State Geologist Indiaini, p. 289, pi. xxiii, figs. 9, 10; 



pi. xxvii, tig. 18. 



1882. StropJiodimta, Whitfield. Geology of Wisconsin, vol. iv, p. 327, pi. xxv, fig. 18. 



1883. Strophodo7ita. Hall. Ann. Rept. N. Y. State Geologist for 1882, pis. xiii (44) ; xiv (45) ; xv (46), 



figs. 1-24. 



1884. Strophodonta, Walcott. Paleontology Eureka Dist., pp. 118-122, pis. ii, xi, xiii. 

 1889. Strophodonta, Nettelrot'h. Kentucky Fossil Shells, ]ip. 142-150. 



1889. Strophomena, Bakrois. Faune du Calcaire d'Erbi'ay, pp. 63-65, 67, \A. iv, figs. 6, 8-10. 



Diagnosis. Shells normally concavo-convex or .subplano-convex. Cardinal 

 area common to the two valves, that of the brachial valve narrower or linear ; 

 smooth or finely striated longitudinally, sometimes showing through the outer 

 laminse of the shell strong, parallel, transverse bars, which project beyond the 

 cardinal margin as short processes, and articulate with a corresponding series 

 of pits in the opposite valve. The earliest species have these denticulations 

 developed only for a short distance on each side of the center, while in the lat- 

 ter faunas they extend the entire length of the hinge-line. In the type-species 

 the delthyrium is usually completely closed by the extension of the shelly laminte 

 of the area, and on the inside by the formation of a callosity between the 

 apophyses of the cardinal process. Sometimes a low, narrow, convex deltidium 

 is present, but in the early species the delthyrium is frequently open. 



From the normal position of the dental lamellae there extend two diverging, 

 sometimes nearly vertical, ridges of variable strength, bounding the post-lateral 

 portion of the muscular area, which is not limited by a ridge in front. The 

 entire muscular area consists of two broad flabelliform diductor scars, enclosing 

 an oval adductor which is distinctly divided into anterior and posterior ele- 



