BELEMNITES OF THE LIAS. 



71 



Observations. In the figure quoted from Quenstedt the lateral striation is not 



DIAGRAM 22. 



I 



represented -. in other figures of Quenstedt referred to B. acnarius Cephalopoda,' 

 pi. xxv), lateral striation is represented, but not the terminal compression. D'Orbigny, 

 pi. vii, fig. 4, represents the retral part of the guard as tubular. These fossils belong to 

 the Upper Lias. At t the winding interior structure is represented. 



On Belemnites allied to b. digitalis of Schlotheim, Plates XV, XVI. 



Few Belemnites appear on a first view more characteristically separate from the rest 

 than the compressed, very blunt, straight-sided forms of the Upper Lias, which are 

 frequent in the continental museums, under the name of B. dicjitalis. In only a few 

 instances is this form exactly discovered in collections of Enghsh specimens. But the 

 use of the term in museums and in books is such as to include a much greater variety 

 of forms than seemed to Blainville and Voltz fairly admissible. Taking the idea of this 

 Belemnite from the text and figiu-es of Voltz, we have a cylindroidal, much compressed 

 form, quite obtuse, and even-rounded to an egg-shape at the end ; and upon making longi- 

 tudinal sections the internal layers, after a certain age, correspond in bluntness of termi- 

 nation. The youngest layers end sharply. The cross section in the forward part of the 

 alveolar region shows a remarkably thickened accretion of the sheath on the ventral aspect. 

 There is always a ventral furrow in one variety, called B. irregularis by Schlotheim ; 

 and indeed the apex being sometimes umbihcate, sometimes papillary, and sometimes in 



