19 

 1864. Nautilus Texanus (?) " Shuraard." (Gabb.)' 

 " Paleontology of California.'" Vol. I., page 59} Plate IX., figures 3^. b. 



There are some reasons for doubting whether the Californian shell, 

 described and figured in the work quoted above, is correctly referred to 

 Dr. Shuniard's species. The siphuncle appears to be placed difterently 

 in the two shells; in N. Texanus (Gabb.), it is said to be situated above 

 the centre of the whorls, as is the case in N. Atlas ; in N. Texanus, 

 (Shuniard) its position is described as below the centre of the volutions, as 

 in N. pseudo-elegans. 



It is niost*likely that N. Kebrascensis, Meek, N. Texanus, Gabb (non 

 Shuniard)^ and the Sucia Island Nautilus are all forms of one variable 

 species. 



The discovery of such forms as Nautilus spirolobus, Dittmar, in the 

 " Hallstadten Kalken " (or Trias) of Eossmoos, near the Lake of 

 Hallstadt,' of i\^. Mojsisovicsi, Neumayr, in the Middle Oolite of Poland, 

 and of theiV. Aspe?', Zittel, a sjiecies closely allied to the present fossil, 

 in the Upper Tithonic beds of Moravia, has recently proved that the 

 ril)bed Nautili are b}^ no means exclusively confined to the Cretaceous 

 rocks, as was formerly supposed. Still, they are eminently character- 

 istic of the Chalk Formation, in which they attained their maximum of 

 development as a group. 



AMMONITES. 



Group /.* — Cli/jjeiformes, D^Orhigny. 



Sub-genus Oppelia, Waagen. — " C4eognostisch-Palceontologisclie Beitrage. " Von Dr. 

 E. W. Benecke. Page 250. Munchen : 1869. 



Ammonites Perezianus. (N. Sp.) 



Plate II., figs. 1 and la. 



(Perhaps a variety of Oppelia Waageni, Zittel. See " Die Fauna der Aelterea Ce- 

 phalopoden Fuehrenden Tithoubildungen," by Dr. Karl Alfred Zittel. Cassel : 1870j 

 Plate XXIX., figs. la. and lb.) 



Shell discoidal, lenticular, thin ; umbilicus small ; surfiice ornamented 

 by broad, faint and transverse folds. 



* The numbers attached to these groups refer only to the present collection. The order is nearly that 

 adopted in the " PaUeor.tologia I ndica," but the Ligati are placed between the Planulati and Fimbriati. 

 instead of before the Planulati. In the case of the Ammonites only, a short definition of the saiieni, char- 

 acters of each species is prefixed to the more detailed description. 



