OBOLIDiE. 371 



Obolus EiCHWALD (in part), 1860, Lethsea roasica, ancienne p6riode, vol. 1, sec. 2, pp. 924-925. (Described in French. 



The species referred to the genus belong with Obolus, Obolus (Acritis), and Obolus (Mickwitzella).) 

 Obolus Eichwald, Davidson, 1866, British Fossil Brachiopoda, vol. 3, pt. 7, No. 1, p. 58. (Gives synonymy and refers 



genus to Lingulidse.) 

 Not Schmidtia von Volborth, 1869, Verhandl. Russ.-kais. min. Gesell. St. Petersburg, 2d ser., pt. 4, pp. 208-209. 



(Characterized and discussed as a new genus to include those forms which had been referred to Ungula, but 



which were not included in UnguUtes Quenstedt, 1837, p. 143. Schmidtia celatus is, however, described as the 



only representative of the new genus.) 

 Obolus Eichwald, Dall, 1870, Am. Jour. Conchology, 2d ser., vol. 6, pt. 2, pp. 154 and 162. (Described.) 

 Ungula Pander, Dall, 1877, Bull. U. S. Nat. Mus. No. 8, p. 75. (Discusses date of publication of Ungula Pander, 



Ungula Rose, and Obolus Eichwald.) 

 Obolus Eichwald, Zittel, 1880, Handbuch der Palseontologie, Bd. 1, Abth. 1, p. 664. (Described in German.) 

 Obolus Eichwald, Davidson, 1883, British Fossil Brachiopoda, vol. 5, pt. 2, p. 218. (Mentioned in discussion of 



Siphonotreta.) 

 UnguUtes Quenstedt, 1885, Handbuch der Petrefactenkunde, Aufi. 3, p. 756. (Characterized in German.) 

 Obolus Eichwald, Oehlert, 1887, Manuel de conchyliologie, by Fischer, p. 1261. (Described in French, with 



figures of "0. davidsoni Salter" and " 0. politus Kutorga.") 

 Obolus MicKwiTz, 1892, Melanges geol. et paleontol. tir6s du Bull. Acad. imp. sci. St.-P6tersbourg, vol. 1, pp. 57-64. 



(Described and discussed in German.) 

 Obolus Matthew, 1892, Trans. Roy. Soc. Canada, 1st ser., vol. 9, sec. 4, No. 5, pp. 43-44. (Translates the descrip- 

 tion given by de Verneuil, 1845, p. 290.) 

 Obolus Eichwald, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, pp. 242-243. 



(Described and discussed.) 

 Aulonotreta Kutorga, Hall and Clarke (in part), 1892, idem, pp. 243-244. (Described and discussed. As discussed 



the genus includes species referred to both Obolus and Obolus {Acritis).) 

 Obolus Eichwald, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum, for 1891, pp. 558-559. 



(Copied from Hall and Clarke, 1892a, pp. 242-243.) 

 Aulonotreta Kutorga, Hall and Clarke (in part), 1892, idem, pp. 559-560. (Copied from Hall and Clarke, 1892a, pp. 



243-244.) 

 Obolus Eichwald, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 80-81. (Described 



and discussed.) 

 Aulonotreta Kutorga, Hall and Clarke (in part), 1892, idem, p. 82. (Described and priority of generic references, etc., 



discussed. As discussed the genus includes species referred to both Obolus and Obolus (Acritis).) 

 Obolus Eichwald, Hall and Clarke, 1892, idem, pp. 337-339. (Gives a translation of Mickwitz's diagnosis, 1892, 



and discusses genus.) 

 Obolus Eichwald, MiCKwnz, 1896, M6m. Acad. imp. sci. St.-P^tersbourg, 8th ser., vol. 4, No. 2, pp. 1-133. (These 



pages contain a general discussion of the genus and its relations, in German, the actual diagnosis of the genus 



being given on pp. 127-129.) 

 Obolus (Euobolus) Mickwitz, 1896, idem, pp. 129 and 133. (Characterized in German, on p. 129, as a new subgenus.) 

 Obolus Eichwald, Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 385-386. (Genus and type species discussed.) 

 Obolus Eichwald, Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 681-683. (Described and discussed, translating 



a portion of Mickwitz's description, 1896, pp. 118-121.) 

 Obolus Eichwald, Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, p. 135. (Characterized 



and discussed.) 

 Obolus (Eoobolus) Matthew (in part), 1903, idem, pp. 135-136. (Characterized as a new subgenus. One of the three 



species referred to the subgenus belongs with Obolus and the remaining two belong with Lingulella.) 

 Obolus Eichwald, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 144. (Classification 

 of genus.) 



Diagnosis (mainly after Mickwitz [1896]). — Shells nearly equivalve, equal-sided, moder- 

 ately convex, subcircular, transversely or longitudinally ovate, in some species subtriangular 

 or subrectangular. 



Shell substance calcareocorneous, structure foliated ; the layers of calcium phosphate alter- 

 nating with homogeneous, horny lamellae are traversed by microscopic canals, which in their 

 main direction are perpendicular to the plane of stratification; the inner layers and lamellae 

 are more or lass oblique to the thin outer layer over the central and posterior portions of the 

 valves, and strongly so with the short lamellae of the anterior and lateral parts. Surface 

 shining as if varnished, with concentric and usually radial striation, varying from bare visibility 

 to deeply incised concentric folds and radial ribs. Color of shell dark grayish blue to black, 

 when in a state of decomposition dark reddish brown to whitish. Front and side margins 

 usually thin, sharp-edged, fragile, lying in the same plane with the hinge margin, which is 

 greatly tlaickened inside. Area mainly in the plane of the edge of the valve, in the ventral valve 

 triangular, owing to the somewhat projecting beak, in the dorsal valve rounded at the point. 



