\ Nil I 





plalo ha- not been a lit horit a t i \ ely -el I led li. \\ t \ r ; lhr\ li;i\ 



been described under the names of Aptychus :in<l Mui> 



bivahe -hells, iiiid have al-o been thought to be ci rri | n- Is ;i IK I 

 f'M-n I lie c;trt ilanes. Li'ixxards or mi/ r<i/l >/ />/</<<,/ cut t le-boiic- ! <!' 

 Ammonite-; but tin- weight of o|>inii)ii is decidedly in favor of 

 rdinir them :is opercula (lirsl, suggested by Kiippell. in I 



In the Ai-irtcs UT<HI|> of Aiuiiioiiites the operculam is a single, 



horny, tlrxiMr pirt-r. whilst in .Mnotiu-i 1 jiToup it, is shelly, consist- 



inu<>t't\v) plntfs joined l>y ;i nieduin sut lire, t he exterior t';iee 

 smooth or striMti'd ami the interior ni.-irked hy u'l'owt h-line^. It 

 is proper to stnte Hint. Ket'erstein , llfonn's K hisseii, iii, !.; 

 al'ter coiisidrriMu: the subject at length. roiK-lu-les that the^e \\civ 

 not operenla. lull does not u'ive a decided opinion as to their 

 t'nnction, although admitting their connection with the Am- 

 inoir 

 The nntei- layer oi' the shell has iieen generally destroyed in 



t'<-il Ammonites, etc., leaving only the inner or nacreous and 

 more indestructible layer, which thus exhibits perfectly the edges 



o!' the >epta: 1ml in some cases it is only the outer hiyer that 

 has been preserved ; and t're.piently when the whole shell has 

 di-appeared. we have perfect (v/x/s of the chambers. The de- 

 composition of the animal has cont ,rilmlel to form those, phos- 

 phates and sulphides generally present in the body chamber, 

 whilst the permeation of water deposits crystals of caicai' 

 spar on the inner walls or sometimes even tills the entire. 

 chaml>er. Cross-sections <>f fossil Ammonites with the chambers 

 tilled with spar, when polished, make beautiful cabinet specimens. 

 Some] hue-*, ax in soi i ie >f t he ( ) il I inee ra t a , t he circumjacent mud 



has invaded the air-chambers, but without entirely filling them, 



! i><' the contraction of the vascular lining has left einptv 

 spaces lietween itself and a portion of the wall of eaeh chamber. 



^//'.-'/rs, .I/';/*,-.' n ml /*'///>'. 



In Nautilus we dist in^ nish the two adductor muscles, by 

 which the animal attaches it-elf to tin- walls of it- shell, and 

 which are united by a hoi n\ <-olla r ; and within the shell i; 

 we may notice on either -ide the impiv^ion- of the-e attaeh- 

 ments. -nnkeii into the pearly walls. On the outer side of the 

 1 



