154 
PALEONTOLOGY OF NEW YORK. 
Genus ZYGOSPIRA, Hall. 1862. 
PLATE LV. 
1847. Atrypa, Orthis ?, Stenodsma, Hall. Palaeontology of N. Y., vol. i, pp. 140-142, 288, pi. xv, fig. 15 ; 
pi. xxxiii, figs. 4, 5; pi. Ixxix, fig. 5. 
1859. Rhynchonella?, Hall. Twelfth Kept. N. Y. State Cab. Nat. Hist., p. 66. 
1860. Atrypa, Hall. Thirteenth Kept. N..Y. State Cab. Nat. Hist., p. 69. 
1862. Zygospira, Hall. Fifteenth Kept. N. Y. State Cab. Nat. Hist., p. 154, figs. 1, 2. 
1862. Zygospira, Billings. Canadian Naturalist and Geologist, vol. vii, ii. 393. 
1862. Atliyris, Billings. Palaeozoic Fossils, vol. i, p. 147, figs. 125-127. 
1863. Athyris, Rhynchonella ? , Billings. Geology of Canada, p. 168, fig. 152; p. 211, fig. 211; p. 212, 
figs. 214-216. 
1864. Stenodsma, Meek and Hayden. Palaeontology of the Upper Missouri, p. 16. 
1866. Rhyndionella, Zygospira, Billings. Catalogue Silurian Fossils of Anticosti, pp. 44, 46. 
1867. Zygospb'a, Hall. Twentieth Kept. N. Y. State Cab. Nat. Hist., p. 267. 
1868. Zygospira, Meek. Geological Survey of Illinois, vol. iii, p. 377. 
1872. Zygospira, Hall. Twenty-third Kept. N. Y. State Cab. Nat. Hist., pi. xiii, figs. 23-25. 
1873. Zygospira, Meek. Palaeontology of Ohio, vol. i, pp. 125, 126, pi. xi, figs. 4, 5. 
1875. Zygospira, Miller. Cincinnati Quarterly Journal of Science, vol. ii, pp. 58, 59. 
1878. Zygospira, U. P. James. The Palaeontologist, No. i, p. 7. 
1879. Zygospira, Ulrich. Journal Cincinnati Soc. Nat. Hist., vol. ii, p. 14, pi. vii, fig. 10. 
1882. Zygospira, Hall. Eleventh Kept. State Geologist of Indiana, p. 305, pi. xxvii, fig. 7. 
1882. Zygospira, Anazyga, Davidson. British Silurian Brachiopoda, Supplement, pp. 122, 128. 
1883. Zygospira, Hall. Transactions of the Albany Institute, vol. x, p. 70. 
1889. Zygospira, Nettelroth. Kentucky Fossil Shells, p. 138, pi. xxxiv, figs. 21-25. 
1893. Zygospira, Winchell and Schuchert. Geological Survey of Minnesota, vol. iii, pp. 465-469, 
pi. xxxiv, figs. 42-48. 
Diagnosis. Shells usually small. Outline subcircular or transversely oval. 
Contour subplano-convex. Surface sharply plicate. Pedicle-valve with a 
median plicated ridge. Umbo narrow and prominent; beak acute and in¬ 
curved. Foramen elongate, rarely apical, enclosed by the deltidial plates. 
Hinge-line long and straight; cardinal extremities rounded. A distinct false 
area is formed by a pair of ridges diverging from the beak toward the cardinal 
extremities. On the interior the teeth are moderately well developed and 
unsupported by dental lamellae. 
The brachial valve is depressed convex in the umbonal region and bears a 
more or less conspicuous median sinus. The hinge-plate consists of two broad, 
stout processes, diverging outwardly, grooved on their summits, and separated 
from each other by a narrow, sharp cleft. They form both the socket walls 
and crural bases, and are supported by a low median ridge. Muscular impres¬ 
sions obscure in the typical species. 
