78 BULLETIN OF THE 



the Paleozoic species. The Nautili of the Silurian, such as Nautilus 

 Bohemicus, Nautilus Sternbergii, Nautilus tyrannus, Nautilus Sacheri, 

 figured by Barrande, have very large umbilical perforations. The 

 Devonian Nautili r like those of the Silurian and Carboniferous, all 

 belong to the group of Imperfecti, and have large umbilici, showing the 

 entire spire.' What is the exact size of the umbilical perforations I 

 cannot state, but doubtless it is in the majority of the species large, and 

 the young whorls rounded as in the Carboniferous and Silurian mem- 

 bers of the same group. 



The Carboniferous forms are distinguished by their highly orna- 

 mented and varied adult shells, as well as by their exceedingly large 

 umbilici. Nearly all of these DeKoninck* has pointed out are charac- 

 terized by a large umbilicus, showing the entire spire. Even the 

 Nautilus oxystomus, a species in which the whorls are considerably invo- 

 lute, has an umbilicus, and at first a rounded whorl, which subsequently 

 becomes hexagonal and then lanceolate in transverse sections, and 

 involute. The umbilical perforation in this species is much smaller 

 than in those species with non-involute whorls. The Museum has 

 among other treasures the entire collection of DeKoninck, and I have 

 been able to verify these observations. 



The species of the Trias and Permian I have been unable to 

 examine. But of the two species figured by King,f N. Freislebeni, 

 and N. Bowerbankianus, one has a closed, or what is generally called a 

 closed, umbilicus, L e. with probably, as in the modern N. Pompilius, 

 a small perforation. N. bidorsatus of the Muschelkalk also has a form 

 like many of the Jurassic species, and a much smaller umbilical per- 

 foration than is common in Carboniferous species. Other species of 

 the Muschelkalk, such as N. mesodiscus, N. Sauperi, N. reticulatus, 

 are as completely coiled, and as involute as any of the Jurassic and 

 succeeding formations. It is probable, therefore, that the earliest gen- 

 eral change in the size of the "^bilical perforation will be found to 

 take place in this formation. 



The Nautili of the Jura, as pointed out by Pictet, j approximate 

 closely to the existing species in the adult stage, and, as DeKoninck 

 has shown, their umbilici are comparatively closed. The young of two 



* Animaux Fossiles, p. 544. 



t Permian Fossils of England, p. 219. 



4 Pictet,Traite (ilthnentaire de Pal^ontologie, 1845, Vol. II. 



