THE CEPHALOPODA 187 



more than half the length of alveolus), e.g. Bel. mucronata 

 (Fig. 54, 4 



Actinocama%* Cenomanian-Campanian (very like the 

 last, but the part of the guard around the alveolus is im- 

 perfectly calcified, and is always more or less destroyed), 

 e.g. A. quadratus (Fig. 54, d). 



C. WITH DORSO-LATERAL GROOVES. 



Aulacoceras* Trias, Ladinic to Noric (phragmocone 

 much longer than the small hastate guard). 



Hastites, Charmouthian-Neocomian (hastate), e.g. Bel. 

 clavatus (Fig. 53,/). 



Pseudobelus, Aalenian-Cenomanian (lanceolate, with 

 very deep lateral grooves), e.g. Bel. Upartitus. 



D. WITH SEVERAL APICAL GROOVES. 



Dactyloteuthis, Domerian-Yeovilian (cylindro-conical 

 up to a certain age, then suddenly elongating into a long 

 tubular apex), e.g. Bel. acuarius (Fig. 54, /). 



Megateitthis, Aalenian-Bajocian (with similar change 

 of shape), e.g. Bel. giganteus. 



E. WITH MEDIAN DORSAL GROOVE. 



Duvalia, Callovian-Neocomian of Mediterranean pro- 

 vince (much compressed), e.g. Bel. dilatatus (Fig. 54, e). 



The typical Belemnoids die out at the end of Meso- 

 zoic time, except in Australia, where they are recorded 

 from Eocene strata. In Europe, there are in the Eocene 

 several forms, mostly very rare as fossils, which may be 

 their descendants strangely modified before final extinc- 

 tion. Greater interest attaches to two collateral stocks 

 which lead to living forms. One of these is the Eocene 

 Belosepia, which forms a link between the belemnites and 

 the recent cuttle-fish Sepia. The siphuncle is greatly 

 widened, the phragmocone is transitional from its typical 

 form to the "cuttle-bone," and the guard is in process 



