138 
PALAEONTOLOGY OF NEW YORK. 
Genus TREMATIS, Sharpe. 1847. 
PLATE IV G, FIGS. 1-20. 
1825. Orbicula, Sowerby. Zoological Journal, vol. ii. 
1842. Orbicula, Emmons. Geological Survey N. Y., Rept. Second District, p. 395. 
1S47. Orbicula, Hall. Palaeontology N. Y., vol. i, p. 100, pi. xxx, figs.lla-d. 
1847. Trematis, Sharpe. Quarterly Journal Geological Society, vol. iv, p. 66 (June). 
1847. Orbicella, D’Orbigny. Comptes rendus, vol. xxv, p. 269 (August). 
1853. Trematis, Davidson. Introduction to British Fossil Brachiopoda, p. 130. 
1855. Trematis, Emmons. American Geology, pt. 2, p. 201. fig. 63. 
1S59. Trematis, Hall. Twelfth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 72. 
1862. Trematis, Billings. Palaeozoic Fossils, vol. i, pp. 52, 53. 
1866. Trematis, Hall. Descr. New Species Crinoidea and other Fossils, etc. 
1866. Discina {Trematis), Davidson. British Silurian Brachiopoda, pp. 69-71. 
1871. Discina {Trematis), Davidson. British Silurian Brachiopoda, p. 344. 
1871. Trematis, Dall. Bull. Mus. Comp. Zoology, vol. iii, No. 1, p. 37. 
1872. Trematis, Hall. Twenty-fourth Rept. N. Y. State Mus. Nat. Hist., p. 221, pi. 7, figs. 22-25. 
(?) 1874. Trematis, Miller. Cincinnati Quart. Journ. Science, vol. i, p. 347. 
1875. Trematis, Hall. Twenty-third Rept. N. Y. State Cab. Nat. Hist., p. 243, pi. xiii, figs. 17-19. 
1875. Trematis, Hall and Whitfield. Geol. Surv. Ohio; Palaeont., vol. ii, p. 70, pi. i, figs. 4-9. 
1875. Trematis, Nicholson. Palaeontology of the Province of Ontario, p. 18. 
1878. Trematis, Miller and Dyer. Contributions to Palaeontology, No. 2, p. 8. 
1889. Trematis, Ulrich. American Geologist, vol. iv, pp. 22, 23. 
Diagnosis. Shell subcircular or transversely oval in outline. Pedicle-valve 
unevenly convex, more or less depressed over the posterior region ; apex at, or 
behind the center; directly beneath it begins the pedicle-fissure, which tran¬ 
sects the shell, vertically widening to the posterior margin with straight or 
outwardly curving edges. Brachial valve evenly convex, with its apex mar¬ 
ginal and slightly projecting. On the interior, the pedicle-valve shows a faint 
median furrow extending from the angle of the fissure to the apex of the shell; 
this groove widens at its apical termination and may represent a point of mus¬ 
cular attachment. The sides of the fissure are often thickened by callosities 
similar to those sometimes seen in species of Orbiculoidea. From the apex 
of the valve extend radiating and branching vascular sinuses. 
In the brachial valve the posterior margin is much thickened and broadly 
grooved to allow the extrusion of the pedicle. This thickening does not take the 
form of a cardinal area or shelf, but is rather a callosity closely appressed against 
the interior surface of the shell, the central portion being projected beyond the 
margin of the pedicle-valve. Directly below and in front of this area are two 
