BRACHIOPODA. 155 



PHOLIDOPS, Hall. 1859. 



PLATE IV I, FIGS. 17-37. 



1820. Patelliies, Schlothkim. Die Pcti-efakteiikunde aiif ihr. .jetziy. Slanil|)unkt. 



1S39. Patella (f), Sowerby. Murchison's Silurian System, p. 62.^, pi. xii, fig-. 14 a. 



1843. Orhicida, Hall. Geology of New York ; Report Fourth District, p. 108, fig. 1. 



1847. Orbicula, Hall. P.nlBeontology of New York, vol. i, p. 290, pi. 79, figs. 7 a, b. 



1852. Orbieida 9, Hall. Palaeontology of New York, vol. ii, p. 250, pi. 53, figs. 4 a, b. 



1855. Orbicwloidea, McCoy. British Palaeozoic Fossils, p. 189. 



1859. Cranhps, Hall. Twelfth Rept. N. Y. State Cab. Nat. Histoi-y, p. 84. 



1859. Pholidops, Hall. Palaeontology of New York, vol. iii, pp. 489, 490. 



1859. Crania, Discina, Salter. Murchison's Siluria, Second Edition. 



1860. PhoUdops, Hall. Thirteenth Rept. N. Y. State Cab. Nat. History, p. 92. 



1862. PhoUdops, Hall. Fifteenth Rept. N. Y. State Cab. Nat. History, p. 195. 



1863. PhcUdo-ps, Hall. Sixteenth Rept. N. Y. State Cab. Nat. History, p. 31. 

 1863. Pliolidops, Hall. Trans. Alb.any lostitute, vol. iv, p. 209. 



1566. Pliolidops, Hall. Descriptions New Species Fossils, etc. ; Advance sheets Twenty-fourth Rept. 



N. Y. State Mus. Nat. History. 

 1866. Crania, Davidson. British Silurian Brachiopoda, p. 80, pi. viii, figs. 13-18. 



1567. Pliolidops, Hall. Palaeontology of New York, vol. iv, pp. 31, 32, 413, 414, pi. iii, figs. 1-11. 



1871. Pliolidops, Dall. Bull. Mus. Coniji. Zoology, vol. iii. No. 1, p. 27. 



1872. Pliolidops, Hall. Twenty-fourth Rept. N. Y. State Mus. Nat. History, p. 221, pi. vii, figs. 8-10. 



1873. PhoUdops, Meek. Geol. Surv. Ohio ; Palaeontology, vol. i, p. 130, pi. v, figs. 2 a, b. 



1879. PhoUdops, Hall. Twenty-eighth Rept. N. Y. State Mus. Nat History, p. 149, pi. xxi, figs. 1, 2. 



1881. PhoUdops, Hall. Eleventh Ann. Rept. State Geologist Indiana, \i. 284, pi. xxi, figs. 1, 2. 



1883. PhoUdops, Davidson. British Silurian Brachiopoda, Supplement, p. 216, pi. xvii, fig. 48. 



1884. PhoUdops, Walcott. Paleontology Eureka District, pp. 113, 114, pi. ii, figs. 6, 7. 



1885. PhoUdops, Verworn. Zeitschr. der deutsch. geol. Gesellsch., vol. xxxvii, p. 173. 



Diagnosis. Shells small, patelliform, equivalve, equiconvex, inarticulate, un- 

 attached. Outline oval or subelliptical ; apex subcentral, excentric or marginal, 

 sometimes terminal and produced. Surface marked by strong, concentric, often 

 lamellose lines of growth, which are crowded on the posterior, and distant on 

 the anterior portions of the valves ; these are sometimes crossed by faint in- 

 terrupted radiating lines. In the interior, the surfaces of contact make a broad 

 smooth, flat or slightly convex border, somewhat broader in front than behind. 

 The muscular and visceral area occupies a sharply defined and very limited 

 space in the apical portion of each valve. In both valves it is of essentially 

 the same size and subtriangular in outline, the apex of the triangle pointing 

 forward and usually surrounded by a conspicuous callosity. 



The ventral (?) valve bears two well defined central adductors occupying the 

 same relative position as in Crania ; these impressions are usually simple, but 



