76 



BRITISH BELEMNITES. 



part of the cone it is -^th. The conotheca is finely striated and broadly undulated across 

 the ventral region, longitudinally striated on the dorsal region, and there marked by a 

 slightly prominent mesial linear band. Fifty-five septa were counted in the space of half 

 an inch from the apex of the phragmocone. 



Observations. This very common Belemnite varies as to the apex, which in young 

 examples is acute, or even a Httle produced, while in old specimens it is always obtuse ; 

 there is always a tendency to greater curvature toward the apex in the ventral than in the 

 dorsal region ; the distinctness of the grooves varies ; especially this is the case with 

 the ventral groove, Avhich is occasionally almost obsolete. Simpson marks two 

 varieties, viz. : 



a. Two grooves and numerous fine strise at the apex, 



b. Three distinct grooves at the apex. 



These varieties occur together in the Upper Lias near Whitby ; I find the striation to 

 occur in both in good young specimens ; the differences as to the ventral groove are such 

 as to unite the whole into one group, though in that particular the extreme examples 

 appear distinct enough. The apex is often eroded, so as to be, in the sense of Blainville, 

 urnbilicate. 



The account of this Belemnite given by Young and Bird requires some elucidation. 

 In the first edition of their work it is illustrated by two figures, one (pi. v, fig. 6) repre- 

 senting the guard engaged in a mass of Pentacrinites from the lower part of the Upper 

 Lias — a fair specimen of Mr. Bird's talents as an artist ; the other (pi. xiv, fig. 1) not so 

 well drawn, but showing the exserted phragmocone. These two figures represent two 

 distinct forms — distinct varieties at least. In the second edition, only one figure is given 

 (pi. XV, fig. 1), and that not so good as either of those previously published. In the text 

 of both editions a careful description is given ; one of the references is to B. elongatus of 

 Miller, certainly an error. The length is said to reach 10 or 12 inches, with a diameter 

 of 2 inches at the broad end, but this must be very unusual. 



Localiti). Whitby, Saltwick, Sandsend, and other places in the Upper Lias of 

 Yorkshire, at various stages above the Jet-beds, up to and including the Leda-beds {Youmj 

 and Bird, Simpson, PhilUjjs). These show two varieties as to length, the axis of the 

 guard being proportionately shorter in fig. 40, and longer in fig. 41. 



Belemnites rudis, n. s. PI. XVI, fig. 42. 



Guard. Short, somewhat compressed, and oval in section, with or without one 

 short obscure apicial groove; no dorso-lateral grooves. Adult specimens blunt at 

 the end. 



Sections across the alveolar region (PI. XVI, fig. s) show the slightly oval outline 



