164 PALEONTOLOGY OF NEW YORK. 



1868. AtryfXh Biu-mos. Geology of Canada, p. 316, fig. 321 ; p. 318. fig. 335 ; p. 384, fig. 416. 



1866. Atrypa, Davidsom. British Devonian Brachiopoda, pp. 53-59, pi. x, figs. 3-13 ; pi. xi, tigs. 1-12. 



1866. Atrypa, Shalrb. Bull. Mus. Comparative Zoology, No. 4, p. 68. 



1867. ./Itrypo, Davidson, British Silurian Brachiopoda, pp. 130-136, pi. xiv, figs. 1-22; pi. xv, 



figs. 1-8. 



1867. Atrypa, Whitfield. Twentieth Rept. N. Y. State Cab. Nat. Hist., p. 141. 



1867. Atrypa, Hall. Palseontology of N. T., vol. iv, pp. 312-327, plates li, lii, figs. 1-12 ; pis. liii, liiiA. 



1868. Atrypa, Mhkk and Worthbn. Geol. Survey of Illinois, vol. iii, p. 430, pi. xiii, fig. 7. 

 1868. Dranatogpira, McChbskby. Ti-ans. Chicago Acad. Sci., vol. i, p. 32, pi. vii, fig. 3. 

 1868. Atrypa, Mkbk. Trans. Chicago Acad. Sci., vol. i, pp. 96, 97, pi. xiii, figs. 12, 13. 

 1868. Atrypa, Hbbk and Worthbn. Geol Survey of Illinois, vol. iii, p. 432, pi. xiii, fig. 11. 



1872. Atrypa, Hall and Whitfikld. Twenty-fourth Rept. N. Y. State Mus. Nat. Hist., pp. 197-199. 



1875. Atrypa, Hall and Whitfibld. Palseontology of Ohio, vol. ii, p. 133, pi. vii, figs. 12-14. 



1877. Atrypa, Mkbk. King's U. S. Geol. Expl. Fortieth Parallel, vol. iv, p. 38, pi. i, fig. 7; pi. iii, fig. 6. 



1878. Atrypa, Ethbridgb. Quart. Jour. Geol. Society London, vol. xxxiv, p. 596. 



1879. Atrypa, Hall. Twenty-eighth Rept. N. Y. State Mus. Nat. Hist., p. 162, pi. xxv, figs. 44-47. 



1880. Atrypa, Whitb. Second Ann. Rept. Indiana Bureau of Statistics and Geol., p 502, pi. v, figs. 7-9. 



1881. Atrypa, Whitb. Tenth Rept. State Geologist of Indiana, p. 134, pi. v, figs. 7-9. 



1882. Atrypa, Hall. Eleventh Rept. State Geologist of Indiana, p. 304, pi. xxv, figs. 44-47. 

 1882. Atrypa, Whitfibld. Geology of Wisconsin, vol iv, p. 333, pi. xxvi, figs. 5-8. 



1884. Atrypa, Walcott. Monogr. U. S. Geol. Survey, vol. viii, p. 150, pi. xiv, figs. 4, 6. 



1885. Atrypa, Fobrbtb. Bull. Denison Univei-sity, vol. i, p. 90, pi. xiii, fig. 9. 



1889. Atrypa, Bbbchbr and Clakkk. Memoirs N. Y. State Museum, vol. i, p. 51, pi. iv, figs. 12-20. 

 1839. Atrypa, Nbttblroth. Kentucky Fossil Shells, pp. 88-92, pi. xiv, figs. 1-23 ; pi. xv, fig. 1 ; 



pi. xxxii, figs. 5-8, 44-47, 64-66. 



1890. Atrypa, Fobrstb. Proc. Boston Society Nat. Hist., vol. xxiv, pp. 314-316, pi. vi, figs. 8, 9. 



Diagnosis. Shells subcircular or longitudinally suboval in outline. Gibbous, 

 strongly inequivalve. Hinge-line short, straight; cardinal extremities rounded. 

 Beaks not prominent. 



Pedicle-valve the smaller ; convex in the umbonal region, but depressed and 

 often deeply sinuate anteriorly. Beak small, usually incurved in advanced 

 growth-stages, concealing the foramen and deltidium. The foramen is triangu- 

 lar in young shells, extending to the hinge-line, but becoming gradually closed 

 by the growth of deltidial plates, and at maturity is circular and apical, en- 

 croaching slightly on the substance of the valve. The plates of the deltidium 

 are not coalesced along the median suture. On the interior the umbonal cavity 

 is short but very broad. The teeth are large, widely separated and doubly 

 grooved, first by an oblique furrow at the base, into which is fitted a crenulated 

 ridge of the other valve, then by a short longitudinal depression on the summit ; 

 the tooth is doubly curved and reflected, making the articulation of the valves 

 very firm. These teeth arise from the inner surface of the lateral slopes of the 



