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PALEONTOLOGY OF NEW-YORK. 
Spirifer disjunctus : Davidson, Quar. Jour. Geol. Society, Yol. 9, pa. 354, pi. 15, f. 1 - 5. 1853. 
« verneuilii : M'Coy, Brit. Pal. Fossils, p. 376. 1852. 
“ disjunctus: Murchison, Siluria, 2d edition, p, 299, f. 4. 1859. 
«« barumensis: Sowerby, MSS.; Salter, Jour. Geol. Society, Yol. 19, p.480. 
Spirifera disjuncta: Davidson, Monograph Brit. Dev. Brachiopoda, p. 23, 1864. 
Delthyris perlata .- Conrad, Ann. Rep. on Palaeontology of New-York, p. 54. 1841. 
•« chemungensis : Conrad, Jour. Acad. Nat. Sciences of Philadelphia, Yol. 8, p.263. 1842. 
<< disjuncta ? Phillips; Hall, Geol. Rep. 4th Dist. New-York, p. 269, f. 3. 1843. 
<< cuspidata: Hall (not Martin), lb., p. 270, f. 1. 1843. 
«< acanthota: Id.. Ib., p. 270, f. 2, 2 a. 1843. 
“ inermis : Id. Ib., p.271, f.4, 4 a; p.270. 1843. 
Compare Spirifer whitneyi, Hall, Geology of Iowa, pa. 502, pi. 4, f. 2. 1859. 
Shell variable in shape, semioval, semicircular or subrhomboidal 1 hinge¬ 
line usually as long as the width of the shell (rarely shorter), with the 
cardinal angles slightly rounded, moderately or extremely extended 
into long attenuated or mucronate points. Valves convex, or more or 
less gibbous : entire surface, including mesial fold and sinus, plicated. 
Ventral valve more or less convex, usually with a regular convexity on 
the sides, but sometimes concave between the margins of the sinus and 
the extremities. The sinus is more or less deeply concave, rarely quite 
shallow, usually rounded but sometimes angular in the bottom, and 
the margins clearly defined : beak elevated and produced, moderately 
incurved over the area, which is flat or concave and of variable height. 
The fissure is often partially closed by an arching pseudo-deltidium. 
Dorsal valve moderately convex, sometimes a little concave towards the- 
cardinal angles : mesial fold distinctly defined, usually of moderate 
elevation and convexity, sometimes, subangular, and often divided by 
a furrow down the centre : area very narrow. 
Surface marked by from twenty to., forty or more simple rounded or 
subangular ribs on each side, with nearly equal interspaces. The mesial 
fold and sinus are each marked by about ten, sometimes twelve or 
fourteen ribs near the front, which proceed from the bifurcation of two 
Or three at the apex of each valve*.. When the shell is perfectly pre¬ 
served, the entire surface is marked by fine contiguous concentric 
striae. 
♦ Mr. Davidson says the increase is by intercalation; but strictly this is rarely true of our specimens. 
