BELEMNITES OF THE LIAS. 



87 



Proportions. The diameter {v d) being taken at 100, the ventral radius is 40, the 

 dorsal 60, the cross diameter 100, the axis 420. 



Phragmocone. Nearly straight, with a nearly circular section ; the angle 

 m = 25°. 



Locality. In the lower part of the Upper Lias at Saltwick {VUllips) ; at Robin Hood's 

 Bay {Cullen) ; in ironstone layers at Kettleness {Simpson) ; in the shale under the Jet- 

 bed, plentifully ; and in ironstone layers at Staithes and Rosedale {Phillips) ; in the Marl- 

 stone series below the ironstone. 



Observations. The agreement of this Belemnite with that long known as B.paxiUosus 

 is obvious and intimate, and the resemblance of particular selected specimens is almost 

 complete, the principal observable difference being a greater proportionate length of 

 axis and a longer tapering to a less obtuse apex in the Yorkshire specimens. 



For comparison, a specimen from Ilminster, in Mr. Moore's Cabinet, is represented 

 fig. 52, Ml. 



Recurvation of the apex occurs in several of the specimens of B. paxillosus, especially 

 in those from Ilminster; in several of the specimens of B. cylindricus from Rosedale, 

 near Staithes, it is so pronounced as to approach the form of B. aduncatus. 



On the whole, I can hardly doubt that the Yorkshire specimens agree with B. 

 paxillosus amalthei of Quenstedt (' Cephal.,' pi. xxiv, fig. 5) ; the state of conservation 

 seldom allows of the striation of the apex to be perfectly seen, as in our representation 

 oi B.paxiUosus (PI. XX, fig. 52, Ml). 



B. elongatus, B. apicicurvatus, B. paxillosus, and B. cylindricus, taken together, com- 

 pose a natural group of generally cyhndrical or cylindroid forms, with dorso-lateral grooves 

 at the apex, and plaits or striae on the ventral and dorsal aspects (exceptionally, a deeper 

 stria on the ventral and also on the dorsal face). They are unknown in Lower Lias, but 

 extend from the base of the Middle Lias to the lower part of the Upper Lias, and arc 

 found in Dorsetshire, Gloucestershire, Northamptonshire, Lincolnshire, and Yorkshire. 



Belemnites oxyconus, Quenstedt. (Diagram, No. 23, p. 88.) 



Reference. Belemnites {tripartitus) oxyconus, Quenstedt, ' Cephalop.,' p. 41 9^ 

 pi. xxvi, figs. 19, 20, 1849. 



Guard. Compressed, conoidal or conical, ending in a produced, pointed, somewhat 

 recHned apex ; lateral grooves extend over the alveolar region. 

 Transverse section oval, the ventral region broadest. 



