EXPLANATION OF PLATE XL 



Fig. 



28. Belemnites tripartitus. (Whitby.) 



V. Ventral aspect. 



d. Dorsal aspect, showing frequent striae. 



/. Lateral aspect. At v, d, is the apex of the alveolus. 



s. Shows cross section at the alveolar apex. 



s". The section near the apex. 



a. The interrupted striation. Specimen in Prof. Phillips's Collection. 



29. Belemnites stjbaduncatus, in various stages of growth. (Whitby.) 



V . Ventral aspect of a young specimen. 



Lateral aspect of the same. 

 d. Dorsal aspect of a very young individual. 



Lateral aspect of a more advanced and more hastate variety. 



The same aspect of one still older. 

 d!" Dorsal aspect of the same specimen. 



The same aspect of one fully grown. 

 s, s", s", s". Transverse sections : s being across the alveolar cavity ; s", at the 

 alveolar apex ; s"\ towards the apex, unusually excentric ; near the 

 apex. 



