i i IM:I i.i 



ti of tin- loud Neocomian, there ua anothei group, th.-ii r 



//'/// . of (Milch \'li 



n, which i> most intimately allied to /,//////.- 7'///"///v/////i; 



IV I lie li'alllt. 



The character of the genii-- may lie defined ->nnc\vli;i1 in the 

 following manner: Lijlni'fi'uliiln . in which :ill the whorl- or ;i 

 part are not in contact : spiral coiled in one plane. M- e\M-rted 

 lor only :i >in:ill i:irt of its COUrse; npp-r I:i1rr:il loin- always, 

 IONVT ni(tl\, (li\i(lc<l into paired 



Ovi-r 101) species. 



Genus TURRILITES, 



Tlie ii'i-eat majority of cretaceous Ammonites not coiled in 

 one plane, which are divided into the irenera Y'///v/7//Vs. //<///*/- 

 \s and //I'fi'rnrcratt. manifest \>y the symmetrical livi>inn 

 of the lateral lolies decided allinit ies with /^//mv/v/s and lln.iiu.l>*; 

 lteside>. the foi'ins least di vei 1 u,'ent from the forms with the spiral 

 in one plane, which are referred to J/rlicoceras, nlso present in all 

 other characteristics Midi a striking agreement with //nmili-x. 

 that their incorporation with that LI'CIIIIS is undoubtedly correct. 

 On the other hand the extreme forms diverge widely from this 

 type, and a new direction of variation is presented, so that full 

 justification exists tor regarding them as ^vnerically distinct. 



The new direction of variation which makes itself apparent 

 in the Tnri'ilites, consists in the divergence from the plane in 

 one coil, and the uradual development, of a spire-shaped shell; 

 since Hi-lirnrt'ra* in the various grades of its divergence from 

 /[(iiiu'fi'fi only represents the various stages on this line, this 

 genus must lie included, as Pictet had already indicated. 

 Finally. H'lcroceras polyplocuin and /it'iintiidmnu represent only 

 somewhat abnormal forms of development of the same type. 



We cannot, however, here place all the cretareoii-; Ammonites 

 which diverge from the spiral in one plane; in the upper Neoco- 

 ii:ian a very -insular form appears, and as far a- is known, 

 divrpjv^ widely from all other forni>, and which is aNo not 

 'oiled in one plane. Imt which is distinguished l>y an asymmet- 

 rical development of the lateral lol.es, namely: // ' r--cras 

 muni. Oi-l... A mm, Orli.. and l>i/ r<-<ittim, Orli., 



which we will place afl ll>-f'-rn,;>rnn in the genii- ' U U-low. 



