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mode of coiling, very variable aspects, owing to the closer coiling 

 of some specimens than of others. 



There is no impressed zone in most specimens at any stage, 

 although there is a slight flattening of the dorsal side and an 

 obvious although very slight modification of the dorsum, which 

 takes place in the most closely coiled shells. 



The whorl in section is closely similar to that of natator and the 

 siphuncle similarly situated. The sutures are similar, with the 

 exception of a faint dorsal lobe that appears in this species. 



The whorls do not touch in some specimens at all (PL xiv, Fig. 

 2); in others they may touch in the neanic and ephebic stages. In 

 some they may become excentric in the gerontic stage, and in 

 others this may occur earlier in the ephebic stage. Very likely 

 there is more than one species included under the name, but it is 

 obvious that they are transitional to Barrandeoceras Sacheri. 

 Barrandeoceras Sacheri. 



Nautilus Sacheri, Barrande (Syst. Si/., PL xxxix). PL v, Fig. 

 11-14. 



Loc, Bohemia. 



The large umbilical perforation is shown and the almost straight 

 form of the ana- and metanepionic substages. The paranepionic 

 substage has sutures with dorsal lobe (Fig. 13) and form with flat- 

 tened dorsum (Fig. 14), precisely like that of the close-coiled forms 

 of Sternbergi in the ephebic stage. In B. Sacheri, however, the 

 coiling is not variable and a contact furrow is invariably formed 

 after contact, which takes place always as in Fig. 1 r, at the apex. 



The sutures in the ana- and metanepionic substages have ventral 

 and dorsal saddles and form in section with similar position of 

 siphuncle to Barrandeoceras natator of the Chazy and resemble 

 Sternbergi only in the paranepionic substage. In the neanic stage, 

 after the impressed zone is generated, the whorls become more 

 compressed and this resemblance is less noticeable. 

 Barrandeoceras tyrannum. 

 Nautilus tyrannus, Barr. {Syst. Si/., PL xxxviii). PL v, Fig. 6-10. 



Loc, Bohemia. 



This species is similar to Sacheri, but has a smaller umbilical per- 

 foration and is somewhat closer coiled, the contact furrow appear- 

 ing sooner and the Siembe?'gi stage of the paranepionic is consid- 

 erably shortened. Its first appearance in the outline of the aperture 

 is shown in Fig. 6 in the paranepionic substage. 



