66 PALAEONTOLOGY OF NEW YORK. 



Genus OBOLELLA, Billings. 1861. 



PLATE II, FIGS. 31-44. 



1847. OrMculaf, Hall. Palfeontology N. Y., vol. i, p. 290, pi. Ixxix, figs. 8a, h. 



1847. Avieula?, Hall. Palajontology N. Y,, vol. i, p. 292, jjl. !xxx, figs. 3a, b. 



18.52. Obolus, OvvBN. Geolog-ical Survey of Wisconsin, Iowa and Minnesota, pp. 501, 631, p\. 1 B. 



1860. Lingula?, Hall. Annual Rejioi't Geological Survey of Wisconsin. 



1861. Oboh'Ua, Billincs. Geology of Vei-niont, vol. ii, p. 946. 



1862. Oholdla, Billings. Geology of Canada ; Palseozoic Fossils, vol. i, p. 7. 



1862. Obolella, Mkek and HaydkiV. Pi-oceedings Acad. Nat. Sci. Phila., vol. xiii, ii. 435. 



1863. Oboldla?, Hall. Sixteenth Kept. N. Y. State Cab. Nat. Hist., p. 133, pi. vi, figs. 17-21. 



1865. Obolella, Meek and Hayden. Paleontology Upx)er Missouri, pp. 3, 4. 



1866. Obolella, David.soic. British Silurian Brachiojjoda, p. 60. 



1871. Di.cellomus, Hall. Advance sheets Twenty-third Rept. N. Y. State C;ib. Nat. Hist. 



1871. Obolella, Billings. Canadian Naturalist and Geologist. 



1872. Obolella, Billings. Araei'ican Joui'nal of Science, vol. iii, p. 35.5. 



1873. Obolella, Ponn. Amei'ican Journal of Science, vol. v, p. 213. 



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



1877. Obolella f. Hall and Whitfield. King's Rept. Exploration Fortieth Pai'allel, p. 205. 



1880. Obolella, Whitfield. Palaiontology of the Black Hills, pp. 339-341. 



1881. Obolella, Fobd. American Journal of Science, vol. xxi, p. 131. 

 1884. OboleUaf, Walcott. Palaeontology Eui-eka Distinct, p. 67. 



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

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



Diagnosis.* Shell inarticulated, ovate or suborbicular, lenticular, smooth, 

 concentrically or radiately striated, sometimes reticulated by both radiate and 

 concentric strise. 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 these, 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 {loc. c.it.) and the emended description of the type- 

 species, 0. chromatica, by the same author in 1876 (loo. cit.). 



