TriE CEPHALOPODA. 
183 
described in the sequel. My late friend, Dr. Oppel, in bis ' Mittheilungen,'^ figured and 
described many species of Ammonites from the " Malm" or upper Jurassic of Germany 
Fig. 47. Fig. 49. 
and Switzerland, in the outer chamber of which the Ajjti/chi are preserved. These fossils 
are very instructive, and teach us that each species had its own special form of Aptyclms 
just as it had its own form of aperture and ornamentation (figs. 47, 48, and 49). 
It is interesting and curious to note the various ideas that have prevailed about these 
bodies. Dr. Scheuchzer^ first noticed the Aptychus, and described it as Concha fossilis telli- 
noides porosa Icevis. Dr. Knorr^ considered the Apfychiis as the valves of Lejjas anatifera, 
with which it has some resemblance in form, but differs in structure. Parkinson* called 
it Triyonellites, and described it " as a slightly rounded, trigonal, thick shell, gaping on 
each side. The anterior margin nearly on a straight line, the posterior in a gently waving, 
and the upper side in nearly a circular direction. The outer surface of each valve thickly 
pierced by foramina, which passing nearly through its substance gives it the cancellous 
appearance of bone, the inner surface smooth, but marked with striae, concentric with the 
upper margin. The hinge completely linear without teeth, there being only an appro- 
priate surface on the anterior margin of each valve for the attachment of the cartilage 
externally. No appearance of muscular attachment." Bourdet,^ of Nievre, considered 
Aptychi to be the palatine teeth of fishes, and proposed the name Ichtliyosayones for these 
fossils. H. von Meyer,^ in his 'Memoir on the Aptychus' described the form struc- 
ture of Aptychus lavis as essentially cellular and entirely different from that of the 
ordinary bivalve shells of Mollusca, inasmuch as the lines of growth are never visible on 
1 ' Palaeontologische Mitiheilungen aus dem Museum des Koenigl., Bayer Staates, 1862, see 
pl.ites Ixviii to Ixxiv. 
2 'Specimen Lithogr. Helvet.,' p. 21, 1718. 
' Lapides diluvii universalis testes,' 1755. 
* 'Organic Remains,' vol. iii, p. 184, pi. xiii, figs. 9 — 12, 1811. 
^ ' Notice sur des Fossiles inconnus,' Paris, 1822. 
" 'Nov. Act. Acad. Goes. Leop.-Car, Nat. Cur.,' xv, 2, p. 125, 1831. 
