138 PALEONTOLOGY OF NEW YORK. 



Genus T RE MAT IS, Sharpe. 1847. 



PI.ATK IVG, FIGS. l->0. 



1825. Orhiriila, Sowekby. Zoological Journal, vol. ii. 



1842. Orbicula, Kmmon.s. Geoloffical Survey N. Y., Rept. Second District, j). 39.5. 



1847. Orbicula, Hall. Palieontolog-y N. Y., vol. i, p. 100, pi. xxx, tig-s. lla-d. 



1847. Trematis, Sharpk. Quarterly Journal Geolou-ical Society, vol. iv, p. C6 (Jnne). 



1847. OrhUdla, D'Orbig.ny. Conipte.s rendus, vol. xxv, p. 'Jl)9 (August). 



1853. Trematis, Davidson. Introduction to British Fossil Bracliiopo<Ia, p. 130. 



185."). TreiiMths, 1'^mmon.s. American Geology, pt. 2, p. 201. tig. 63. 



18511. I'remath, Hall. Twelfth Aiui. Rept. N. Y. State Cab. Nat. Hist., p. 72. 



1862. Treinatli, Billings. Palaeozoic Fossils, vol. i, pp. 52, 53. 



18BB. Trematis, Hall. Descr. New Species Crinoidea and other Fo.ssils, etc. 



1866. Ditdna {Trematis), Davidson. British Silurian Braehiopoda, ])p. 69-71. 



1871. Discina (Treiiuitis), Davidson. British Silurian Braehiopoda, p. 344. 



1871. Trematis, Dall. Bull. Mus. Coniji. Zoology, vol. iii. No. 1, p. 37. 



1872. Trrmatis, Hall. Twenty-fourth Rept. N. Y. State Mus. Nat. Hist., p. 221, pi. 7, figs. 22-25. 

 (?) 1874. Trematis, Millkk. Cincinnati Quart. Journ. Science, vol. i, p. 347. 



1875. Trematis, Hall. Twenty-third Rept. N. Y. State Cab. Nat. Hist., p. 243, pi. xiii, tigs. 17-19. 



1875. Trematis, Hall and Whitfield. Geol. Surv. Ohio ; Palseont., vol. ii, p. 70, i)l. i, figs. 4-9. 



1875. Trematis, Nicholson. PaliEontology of the Province of Ontario, p. 18. 



1878. Trematis, Millkk and Dyer. Conti-ibutions to Paleontology, No. 2. p. 8. 



1S89. Trematix, Vlrich. 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 



