MOLLUSCA — CEPHALOPODA . 
155 
animal is the familiar cuttle-bone (Fig. 85 c). Viewing it 
from the back one sees at its end a small point (the inucio) Table-case 
coiTesponding to the guard, and in front stretches a bioad i. 
shelly plate,” like a pro-ostracum. This, however, when 
viewed from the other side, is seen to be cov’ered by a mass 
c 
a b d e f g h i 
Fig. 85. — The Bolemiiito and its Descendants. Sections through the 
middle of the shells, all in the same position, a, a bclomnitc ; b, Spiru- 
lirostra ; c, Spirilla ; d, Belosepia ; c, Sejyia ; /, Belemnoteiithis ; 
g, Conoteuthis ; h, Ommastrephes ; i, a squid. In all figures, p.o. is 
pro-ostracum ; si, siphunclo ; and g, guard. The shell-wall and septa 
are represented by thick black lines. 
of thin shelly plates, which correspond to the septa more 
clearly seen in Belosepia. 
Another Eocene fossil that appears to be descended from 
the belemnites is Spirulirostra (Fig. 85 h). In some of the 
later belemnites may already be observed a shortening of the 
guard and a curvature of the ])hragmocone, processes which 
tend to reduce the unnecessary length of the shell. In 
