184 THE LIAS AMMONITES. 
the internal sniface of the valve, that surface being covered with a nacreous layer, which 
retains the muscular and pallial impressions of the animal. In the Aptj/chus we never 
see these impressions on the inner, whilst the lines of growth are visible on the external 
surface. M. Voltz^ attempted to prove that the Apfyclius v\^as the operculum of an 
Ammonite, because it resembled the opercula of Gastropods in the structure of its 
shelly laminae, and the style of its lines of growth, and likewise because it was frequently 
found in the last chamber of the shell ; and this opinion was held by Professors 
Riippel, Qnenstedt, and Deslongchamps, on the Continent, and by Professors Owen, 
Morris,^ and Dr. Woodward,^ in England. M. Deshayes* contended that the Ajdyclms 
was not the operculum of an Ammonite, but belonged to some of the internal organs 
of the animal, probably the inner walls of the stomach. M. Coquand'' regarded the 
Apfyclius as the analogue of the internal osselets of some Dibranchiate Cephalopods, 
as the Tetidopsis, and thought the two genera ought to be grouped in the same family. 
This author had found specimens where the two halves of the Apfyclius were united and 
formed a single bilobed body, traversed in the middle by a carina, and this he 
compared to the stem of the osselets or pen of the Tetidopsis (figs. 47 and 49). The lines 
of growth and absence of muscular impressions M. Coquand considered to be important 
analogies in support of his views. 
Professor Pictet,'' after reviewing the opinions expressed in the different works already 
cited, and giving the results of his own studies on the Apfyclius, avowed that amidst all 
these diverse opinions it was difficult to pronounce upon the true affinities of these singular 
fossils, which he grouped into three sections : 
1st. The CoRNEi, with a thin, smooth, horny shell ; all from the Lias and Inferior 
Oolite. 
2nd. The Imbricati having the same horny plate, but covered by a calcareous test, 
with large folds representing an imbrication ; these are found from the Lias up to the 
Craie mameuse {etage furoiiien) of the Cretaceous Pormation. 
3rd. The Cellulosi the thickest of all. The horny lamina is covered by a 
cellular layer, which resembles the structure of certain Madrepores, and this cellular 
portion is again covered by a smooth compact deposit. This group is found in the 
Oxfordian stages of the Jurassic Rocks, and extends upwards into the Upper Greensand 
of the Cretaceous Formation. 
Keferstein''' thought these bodies were sexual characters, and suggested that the 
Apfyclius formed the protector to the nidamentary gland in the female Ammonite ; and 
1 'Mem. de la Soc. d'Hist. Nat. de Strasbourg,' t. li, 1836. 
2 Note on Aptychus in 'Ann. and Mag. Nat. Hist.,' vol. x (2ik1 series), p. 356, pi. v D, fig. 1, 1S52. 
3 ' Manual of MoUusca,' p. 80, 1851. 
'Mem. Soc. Geol. de France,' t. iii, p. 31, 1838. 
5 ' Bull, de la Soc. Geol. de France,' t. xii, p. 3/6, 1841. 
<5 'Traite Element, de Paleontologie,' t. ii, p. 385, 1845.' 
^ ' Bronu's Klassen und Ordnungen des Thier.,' Ill I, tab. 113, 1860. 
