EVOLUTION in 



the close of the Cretaceous period the whole group 

 died out after experimenting in every type of shell- 

 form in the effort to survive. 



Nothing is at present known of the embryonic 

 development of Nautilus, and we do not, consequently, 

 know if the primitive embryo shell differs in any 

 respect from the adult ; but the fact that the earliest 

 Cephalopods had straight shells, and that the line of 

 development led through curved to coiled forms is 

 suggestive, and raises the speculation whether the 

 primitive Gastropod shell may not also have been 

 straight, and this phase in its development sub- 

 sequently suppressed in its embryonic history. 



Following up the scale of geological time, we meet 

 with the first of the Decapods (A ulacocevas, belonging 

 to the family Belemnoteuthidse) in the Trias. It is 

 interesting to note that, in the same series, the 

 earliest Gastropod referable to the Tectibranchia, a 

 species of Bullinella, is also recorded, so that we 

 have a Cephalopod with an internal shell comparing 

 in time with a Gastropod of a group that only sub- 

 sequently in the Chalk period achieved a partially 

 internal shell (Philine). 



The Myopsida, or next higher tribe of Cephalopoda, 

 began in the Lias (Geoteuthis and Beloteuthis), while 

 in the Cretaceous of Lebanon the oldest known 

 Octopod, Palceoctopus Newboldi, makes its appearance 

 just as the Belemnites and Ammonites disappear 

 from the scene. 



