66 PALAEONTOLOGY OF NEW YORK. 



Genus OBOLELLA, Billings. 1861. 



PLATE II, FIGS. 31-44. 



1847. OrUcidaf, Hall. Palffiontolo^ N. Y., vol. i, p. 290, pi. Ixxix, figs. 8a, b. 



1847. Avicidah Hall. Palseontology N. Y., vol. i, p. 292, pi. Ixxx, figs. 3a, b. 



1852. Obnlit.i, OwESf. Geological Survey of Wisconsin, Iowa and Minnesota, pp. .501, 631. pi. 1 b. 



18(j0. XiX<77t;a.». Hall. Annual Report Geological Survey of Wisconsin. 



18t)l. Obolclla, Billings. Geology of Vermont, vol. ii, p. 946. 



1862. Oboklla, Billings. Geology of Canada ; Palaeozoic Fossils, vol. i, p. 7. 



1862. OboUUa, Meek and Haydk.v. Proceedings Acad. Nat. Sci. Phila., vol. xiii, p. 435. 



186-3. Oboklla f. Hall. Sixteenth Rept. N. Y. State Cab. Nat. Hist., p. 133, pi. vi, figs. 17-21. 



18i>."). Obohlla, Meek and Haydex. Paleontology Upper Missoun, pp. 3, 4. 



1806. Oboldla, Davidson. Bi-itish Silurian Brachiopoda, p. 60. 



1871. Dkellomm, Hall. Advance sheets Twenty-third Rept. N. Y. St.ate Cab. Nat. Hist. 



1871. Obolclla, Billings. Canadian N.aturalist and Geologist; 



1872. Gbohlla, Billings. American Journal of Science, vol. iii, p. 355. 



1873. Oboklla, Ford. American Journal of Science, vol. v, p. 213. 



1876. Oboklla, Billings. American Journal of Science, vol. xi, p. 176. 



1877. Oboklla f, Hall and Wiiitfibld. King's Rept. Exploration Fortieth Parallel, p. 205. 



1880. Oboklla, Whitkield. Paheontology of the Black Hills, pp. 339-341. 



1881. Oboklla, FoKD. American Journal of Science, vol. xxi, p. 131. 

 1884. Oboklla?, Walcott. Palaeontology Eureka District, p. 67. 



1886. Oboklla, Walcott. Bulletin No. 30, U. S Geological Survey, pp. 109-119. 

 1889. Obulella, Walcott. Proc. U. S. National Museum, vol. xii, p. 36. 



Di.\GNOSis.* Shell inarticulated, ovate or suborbicular, lenticular, smooth, 

 concentrically or radiately striated, sometimes reticulated by both radiate and 

 concentric striae. Ventral valve with solid beak and a small, more or less 

 distinctly grooved area. In the interior of the ventral valve there are two 

 elongated, sublinear or petaloid muscular impressions, which extend forward 

 from near the cardinal scars, sometimes to points in front of the mid-length of 

 the shell. These are either straight or curved, parallel with each other or 

 diverging toward the front. Between the.se, at about the middle of the shell, is 

 a pair of small impressions, and close to the hinge-line a third pair, likewise 

 small, and often indistinct. There is also, at least in some species, a small pit 

 near the hinge-line, in which the groove of the area seems to terminate. 



The dorsal valve has a small, nearly flat hinge-facet ; the minute beak is 

 slightly incurved over the edge of the area. Beneath the beak there is a small 

 subangular ridge, on each side of which there is a cardinal (?) scar. The elon- 



* Derived from Mr. E. Billings' diagnosis in 1872 (foe. nit) and the emended description of the type- 

 species, 0. chromatica, by the same author in 1870 (loc. Ht.). 



