i88 



PALEONTOLOGY 



of reduction to the little point of a modern Sepia. The 

 other transitional form is the Miocene Spirulirostra, in 



\j 







FIG. 54. BELEMNITES. 



a, Pachyteuthis explanatoides (Pavlow), Upper Jurassic, b, Cylindro- 

 teuthis magnificus (d'Orbigny), Lower Portlandian. c, Belemnitella 

 mucronata d'Orbigny, Campanian (Upper Chalk), showing alveolar 

 slit and groovings of surface, d, Actinocamax verus Miller, Cam- 

 panian (Upper Chalk). Dotted lines indicate the destroyed part of the 

 guard, e, Duvalia lata (Blainville), Neocomian. Some species of 

 Duvalia are more compressed than this (e'). f, Dactyloteuthis acuarius 

 (Schlotheim), Charmouthian. Longitudinal section, showing sudden 

 change of shape and cavity (black), a-c , Ventral views ; d,f, sections ; 

 e, side view ; a'-e' , cross-sections. (All x Jd.) (a, b, After Pavlow ; 

 c, e,f, after d'Orbigny ; d, after Crick.) 



which the phragmocone is a more decided cyrtocone 

 than in any belemnite : this leads to the recent Spirula, 

 a gyrocone in which all trace of guard has disappeared. 



