EXPLANATION OF PLATE XXIX. 



Fig. 



71. Belemnites sulcatus. Specimens from the Oxford Clay at Summertown, 



near Oxford. 



V. Ventral aspect of a full-sized specimen ; the groove somewhat less dis- 

 tinctly marked than in other cases, and slightly interrupted. 



v. A yomiger specimen, showing a more marked change of depth in the 

 ventral furrow and its continuation over the alveolar region ; s, cross 

 section of the alveolar region of the guard, depressed. 



s'. Longitudinal section, from back to front, showing the phragmocone 

 i/i situ, its apicial spherule, and a short lanceolate canal, formed by the 

 decomposition of laminae, as shown in a'. 



s". Another longitudinal section showing very similar facts ; the canal 

 somewhat more extended in a". 



s. Cross section of the guard, showing the inflection of the laminae to form 

 the ventral groove, and lacunar of a remarkable kind. 



72. Young specimens from Summertown, near Oxford ; /, lateral ; v, ventral aspect ; 



s', alveolar cross section, nearly round ; s", post alveolar section, nearly round ; 

 ill, magnified surface, the shell dotted with granules, and covered by a partially 

 fibrous layer. Such a layer occurs on some Australian and on some Indian 

 Belemnites. 



73. Youngest examples which occur near Oxford, at Cowley, and Long Marston ; 



y, ventral aspect, the groove distinct on the alveolar region; y', the still younger 

 shell ; alveolar cross section. 



