82 



BRITISH BELEMNITES. 



may in that case be accepted, as a just tribute to one of the best of Belemnitologists. 

 We should then have — 



Belemnites Voltzii, var. conicus, PI. XVII, fig. 43. 



„ var. ventralis, ,, figs. 44, 45. 



„ var. inoi'natus, PI. XVIII, fig. 46. 



In coming to this conclusion we might be confirmed by some other instances of the 

 variability of the ventral sulcus, and it appears to me very interesting and significant 

 to notice the loss of this furrow in passing from the upper part of the Lias to the lower 

 part of the Oolites, which is immediately superposed, while above these lower beds no 

 Liassic forms recur, but a new series of Belemnites begins. In general form we may 

 remark in some specimens convex outlines in the retral slopes of the ventral and dorsal 

 faces near the apex, in others this same part is quite straight-sided, or even a little 

 produced, so as to approach the figure of B. longisulcatus of Voltz (pi. vi, fig. I). But 

 a more important circumstance, already mentioned, is the presence or absence of the 

 ventral groove. In the very uppermost part of the argillaceous Lias beds of Whitby, 

 which contain Leda ovmn, I found specimens all sulcated on the lower side ; in the lowest 

 sandy Oolitic Dogger of Blue Wick I found others not sulcated — this being the main 

 difference which I observe. In a series of these Belemnites lately collected for me by 

 Mr. Peter Cullen the same fact appears. On examination it appears that striation of 

 the apex commonly accompanies the ventro-sulcate variety, and commonly is absent from 

 the other. What appear to be rather young examples of both forms are frequent in 

 all the Upper Lias beds of Whitby, but large specimens are rare there. The younger 

 examples are very acute at the end, the older specimens commonly obtuse or worn or 

 truncated, just as Voltz represents his examples from Giindershofen. 



Belemnites longisulcatus, Voltz. PI. XIX, fig. 47. 



Reference. Belemnites longisulcatus, Voltz, 'Belemn.,' p. 57, pi. vi, fig. 1, 1830. 



B. acuarius longisulcatus-, Quenstedt, 'Cephal.,' p. 412, pi. xxv, f. 23, 1849. 



Guard. Conoidal, straight-sided, much elongated, much compressed, rounded at 

 the end, with two dorso-lateral furrows, three dorsal, and five ventral plaits ; the dorso- 

 lateral fuiTOWs occupy more than half the length, the plaits one fourth of the length ; 

 axis subcentral. 



Transverse section oval, axis but little excentric ; taking the diameter at the 

 alveolar apex as 100, the axis is 500 or GOO. 



