Contributions to Paleontology. 365 
Of questions formerly doubtful and here apparently settled, 
that of the relations of the fossils, known under the names Z7i- 
gonellites or Aptychus, is especially noticeable. These have been 
regarded as peculiar organisms, shells of Lamellibranchiates, 
B 
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® 
p 
after the jaws of Nautilus had been made _ For 
10 Intimate connection with Ammonitide and Goniatitide, what 
niatitide and Ammonitide being admitted, we might then ex- 
pect to find analogous jaws in the latter, and it might be supposed 
that the search for such, would have soon culminated in the con- 
clusion that Trigonellites represented them. The demonstration 
thereof could not, however, have been considered complete, till 
i Ww 
competent observer concerning their relations. Many paleontol- 
ogists of late seem to have been prepared to assent to the opin- 
lon that Aptychus represented an operculum of Ammonites, and 
in figures it has been represented as fitting into and closing the 
apertures of Ammonitids with an admirable exactness,* but per- 
haps accuracy has, in such cases, been unintentionally somewhat 
, i tly applied to the walls of 
the Rina apie va pron antag te prer'ng ‘ectunded beyond the 
aperture of the adult which is much contracted by the inflection of the margin, as 
in A. micrastoma, A. Humphriesianus, A. Codomensis, A. Gervillii, é&e. Tn this di- 
rs ied acco: 
Closely related ones—assump : on, woul 
ciently brave to entertain the privilege of assuming that the duplication of 
ptychus” was aptation to ensure its folding, for extrusion would even 
ed to ted from the distal as well as 
us, as the aperture is contract 
Am. Jour. Sct.—Srconp SERIES, You. XLIII, No. 129.—May, 1867. 
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