184 THE LIAS AMMONITES. 



the internal surface of the valve, that surface being covered with a nacreous layer, which 

 retains the muscular and pallial impressions of the animal. In the Aptychus we never 

 see these impressions on the inner, vi'hilst the lines of growth are visible on the external 

 surface. M. Voltz^ attempted to prove that the Aptychus was 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, Quenstedt, and Deslongchamps, on the Continent, and by Professors Owen, 

 Morris,^ and Dr. Woodward,^ in England. M. Deshayes* contended that the Aptychus 

 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 

 Aptychus as the analogue of the internal osselets of some Dibranchiate Cephalopods, 

 as the Teudopsis, and thought the two genera ought to be grouped in the same family. 

 This author had found specimens where the two halves of the Aptychus 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 Teudopsis (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 Aptychus, 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 CoRNEX, 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 marneuse {etage turonien) of the Cretaceous Formation. 



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 

 Aptychus 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. 



^ Note on Aptychus in 'Ann. and Mag. Nat. Hist.,' vol. x (2nd series), p. 356, pi. v D, fig. 1, 1852. 



3 'Manual of MoUusca,' p. 80, 1851. 



* 'Mem. Soc. Geol. de Trance,' t. iii, p. 31, 1838. 



5 ' Bull, de la Soc. GM. de France,' t. xii, p. 376, 184). 



6 'Traite Element, de Pal^ontologie,' t. ii, p. 385, 1845. 



' ' Bronu's Elassen und Ordnungen des Thier.,' Ill I, tab. 1 13, ISCO. 



