BELEMNITES OF THE LIAS. 



35 



Vaeieties. a. Lateral grooves distinct (fig. 2, d', h'"). 



/3. Lateral grooves obsolete (fig. 2, h"\ and Sovi^., 'Min.Con.,' t. 590, fig. 6). 



Observations. In general form this species difiers very sensibly from B. acutus, 

 as given in these pages ; in the transverse section not less so, this having the apex of the 

 phragraocone almost exactly in the centre of the figure, which would be pretty regularly 

 oval but for the flattened sides. Eacettes, or grooves, are almost always traceable on the 

 flattened sides, and seldom absent from the apex on the dorsal aspect. They are, how- 

 ever, often obscure enough to escape uncritical observation. With B. digitalis it agrees 

 in some degree as to general figure, but as to the proportions of the ventral and dorsal 

 radii of the sheath, and as to the form and situation of the phragmocone, not at all. 

 Very many of the specimens have a rough striation about the apex, arising from some 

 decay there ; and, from the same cause, a sort of umbihcal depression occurs in place of 

 the original apex, which in the young state was obtuse- angled and entire. 



It is necessary to add an additional figure (Diagram 16) for the purpose of pre- 

 venting mistake when some apparently even-smfaced specimens, with a very symmetrical 

 outline, occur. In most of my drawings especial care is taken to make the groovings 

 fully as evident as they appear in the objects. Eor this purpose the light is made 



DIAGRAM 16. 



incident at a lower angle than is usual, so as to mark the longitudinal undulations with 

 distinct Hght and shade. If this be not done many Belemnites may be regarded as "with- 

 out grooves," which yet really are furrowed. In the ordinary light such specimens as 

 those in PI. I, fig. 2, I' and I", would not appear quite so strongly furrowed, and others, 

 like that in Diagram 16, may be thought to be perfectly smooth. 



