BRACHIOPODA. 43 



become obliterated by subsequent overgrowth, but this assumption has yet to 

 be verified. That maturity induces a modification of the deltidium is evinced 

 by the internal median thickening of this plate in C. alta. 



Genus CYRTINA, Davidson. 1858. 



PLATES XXVn, XXXIX. 



1852. Spirifer, Hall. Palaeontology of N. Y., vol. ii, p. 266, pi. liv, fig. 7. 



ISSi). Oyrtia, Shdmard. Geology of Missouri, p. 204, pi. c, fig. 3. 



1857. Ch/rtina, Hall. Tenth Rept. N. T. State Cab. Nat. Hist., pp. 64, 165, 166. 



1858. Cyrtia, Hall. Geology of Iowa, vol. i, pt. ii, p. 512, pi. v, fig. 2. 



1858. Cyrtina, Davidsox. Monogr. British Carboniferous Brachiopoda, p. 66. 



1859. Oyrtia, Hall. Pateontology of N. Y., vol. iii, pp. 206, 429, i)l. xxiv, fig. 1 ; pi. xcvi, figs. 1-6 ; 



pi. xcviii, fig. 8. 



1860. Cyrtia, Swallow. Trans. St. Louis Acad. Sci., vol. i, pp. 647, 648. 



1861. Cyrtia, Billisqs. Canadian Journal, vol. vi, new ser., p. 262, figs. 80-82 j p. 263. 



1862. Cyrtia, WnrrB. Proc. Boston Soc. Nat. Hist., vol. ix, p. 25. 



1863. Cyrtia, Billihos. Canadian Naturalist and Geologist, vol. viii, p. 37. 

 1S63. Cyrtia, Billikos. Geology of Canada, p. 384, fig. 415. 



1867. CyrtiTia, Hall. Twentieth Rept. N. Y. State Cab. Nat. Hist., p. 251. 



1867. Cyrtina, Hall. PaljBontology of N. Y., vol. iv, pp. 263-270, pi. xliv, figs. 26-55. 



1868. CyHina, Mbbk and Worthkn. Geol. Survey of Illinois, vol. iii, pp. 383, 436, pi. vii, fig. 3 ; 



pi. xiii, fig. 4. 

 1868. Cyrtina, Mbbk. Trans. Chicago Acad. Sci., vol. i, pp. 97, 99, 100, pi. xiv, figs. 5-7, 8, 10. 



1873. Cyrtina, Nicaoisoir. Palieontology Province of Ontario, p. 83. 



1874. Cyrtina, Billihos. PalaK)zoic Fossils, vol. ii, p. 49, pi. 3a, fig. 6. 



1874. Cyrtimi (?), Rathbdw. Bull. BuflTalo Soc. Nat. Science, vol. i, p. 242. 



1875. Cyrtina, Hall and Whitfibld. Twenty-seventh Rept. N. Y. State Mus. Nat. History, pi. ix, 



figs. 14-16. 

 1884. Cyrtina, Walcott. Monogr. D. 8. Geol. Survey, vol. viii, pp. 146, 147, pi. iii, fig. 2. 



1888. Cyrtina, Herbick. Bulletin Denison University, vol. iv, p. 14. 



1889. Cyrtina, Nbttblroth. Kentucky Fossil Shells, pp. 95, 96, pi. xiii, figs. 4-16, 21-24. 

 1889. Cyrtina^ Simpson. Trans. American Philosophical Society, p. 439. fig. 4. 



Diagnosis. Shells usually of small size and semipyramidal contour. Pedicle- 

 valve with a high, vertical or arched cardinal area, which may be unsymmetrical 

 from distortion or unequal lateral growth ; this area is divided medially by an 

 elongate-convex deltidium, which may be perforated at any point below the 

 apex, by a circular, direct or oblique foramen, or be without any evidence of 

 such foramen. When present the foramen is accompanied by a sinus on the 

 deltidium, extending from it to the apex of the valve ; even when this foramen 

 has been closed from senile deposition of testaceous matter this foraminal 

 groove mayl^remain. 



