OKI.KK II 



AMMONOIDKA 



540 



Fl'.. llll. 



similar to the hood of .V- "//////>-, and protected the animal when it nrasretJ 



into the living chamber. \\ hen composed of a .-ingle 



piece, the plate is called an anaptychui ; in such cases it 



is invariably carbonaceous, and was doubtless horny in 



the living animal (Fig. 1111). The anaptychufl is rare 



in the Palaeozoic, and has not yet Keen found in the 



Trias, but occurs among the Ari> !>>/" and Amolfhcidcu 



of the Lower Jura. The operculum, when formed of 



two plates, is termed an aptychwi, and is always of 



calcareous composition. It is noteworthy that these 



plates occur uniformly in the same position among ff^ 



some species from certain localities, inside the living 



chamber and close to the venter (Figs. 1110, 1112), a circumstance that led 



Waagen to suppose tln-y 

 served to protect the nida- 

 mental gland of female 

 As shown by 

 in Oppelia, even 

 the embryonic 

 shells were fur- 

 nish e d with 

 aptychi. 1 



Aptychi arc 

 composed of 

 three layers, of 

 which the middle 

 one is the thickest 

 and exhibits a 

 cellular struc- 

 ture, whereas the 

 Detached apiychi 



shells. 

 Michael 



Fl:. 1112. 



Lias 



Hari>iwi-<i* Lytliense, s,>\vb. sp. Upper Li 

 Boll, Wiirtemberg. Aptychus in living 

 chamber. 



Fio. 1113. 



.<ni/ili ifi < *i>iniiji-i 



Upper Cretaoeoaa ; ^ 



Wi-stplialia. D. 'I 

 aptycluis. 



Slll ; ll ,'V 



i_/O6sieiu, 



ched 



1115). 



two outer layers are comparatively dense (Fig. 



have been classified by Zittel 



into several groups according to 



their structure. Celhdosi (Fig. 



1114) are smooth, thick plates, 



with punctate external surface ; 



fmln-ii-ati (Fig. 1110) have the 



surface traversed by oblique 



folds or costae ; Punctati (Fig. 



1115, C) have rows of punctae 



and overlapping folds ; Grunnlnsi 



include thin plates having the 



external surface covered with 



concentric folds or rows of 



tubercles or spinules : Rugosi 



,-,- -. , * . , . ! | Aptychus Uuvi8,\. Meyer. 



are thick plates with irregularly Havana. A, Kxt.-n.ai asi,,-.-t : /;. int.-n.ai, ' . 



arranged granules or rows of 



nodes on the outer surface ; Nigrescentes (Fig. 1112) are covered with a thin 



1 Michael, R., Zeitschr. leutsch. geol. Ges., XLVI. p. 697, 1894. Retn,>-ki, <>.. NYm-s .laln-1,., 

 II. p. 220, lB9l.BlacH- HI l Y, 11. /'., (Ie..l. .Mag. [4], III. j.. 529, 1896. 



VOL. I 2 N 



FIG. 1114. 



Litho-i-aphir Sla1.-> ; SulrnhuS-n. 



