REPORT OF THE STATE PALEONTOLOGIST I9O3 



317 



as 



The protoconch or earliest embryonic stage is not preserved.^ 

 Its former presence outside of the initial apical cone of the shell 

 is clearly indicated by the perforation of the apical end and the 

 opening of the endosiphotube. 



The growth stages of the animal of C. brainerdi 

 recognized in the shells, are characterized by 

 the successive forming of the apical cone, of 

 the chambered portion, the filling of the 

 siphuncle and the formation of the final 

 endosiphosheath [see text fig.i6-i8]. The 

 shell (protoconch) in which the embryonic 

 stage was passed has not been preserved. 

 The first shell which could be preserved was 

 an open small cup which grew out into a 

 long cigar-shaped open conch, the preseptal 

 or apical cone, or nepionic bulb of Hyatt [see 

 text fig. 16, 19]. It was originally entirely 

 filled by the animal and its wall consisted 

 only of the present outer conchiolinous 

 periderm. The aseptate stage is in Nanno 

 termed the ananepionic stage by Hyatt. In 

 C. brainerdi it must have extended 

 through a considerable period of the life 

 of the animal if we can use the length of 

 the preseptal cone as an indicator of the 

 lapse of time. 



The metanepionic substage in Nanno is 

 characterized by Hyatt as that with septa 

 and a huge empty siphuncle, while the paranepionic stage is that 

 with the first endocone and an endosiphuncle formed at the apex. 

 The formation of the first cameras in V a g i n o c e r a s b e 1 e m - 



Fig. 19 Vaginoceras 



belem nit if or m e Holm 

 (sp.) Section of apical part 

 showing the nepionic bulb, first 

 cameras, cicatrix [c], endosi- 

 photube [ec] remains of endosi- 

 phosheaths [e^] and long septal 

 necks, characteristic of Vagino- 

 ceras 



^Several authors have at first considered the large apical cone of 

 Nanno aulema and of Va g i n o c e r a s belemnitiforme as 

 a protoconch. But the finding of the opening of the endosiphotube at 

 the apical end in both species and of a cicatrix at this opening in the 

 closely related Piloceras (by Foord) leave no doubt that the protoconch in 

 these forms has not been capable of preservation. 



