BELEMNITES OF THE LIAS. 



65 



Phragmocone. Much extended under an angle at first of 24°, and afterwards of 

 18°.^ Septa formed of one lamina, elliptical, with axis as 100 to 110, numerous 

 (60 or more) ; depth of chamber, of the diameter ; inner lateral surface of the chamber 

 smooth and flat below the septa. Conotheca slightly undulated in rings, a little concave 

 opposite each septum, a little convex between the septa. The septal outline is waved, 

 and descends to the siphuncular border. 



Greatest diameter observed, 1*6 inch; greatest length, 4^ inches ; in this case the axis 

 of the guard is about 2i inch, and there are about 50 septa. 



Locality, llrainster, in Upper Lias, abundant, and of all ages {Moore). Dundry, 

 full-grown. Upper Lias {Bristol Museum). Glastonbury {Phillips). Kimberley's Brick- 

 yard and Workhouse Yard, Banbury, in Upper Lias, with Ammonites communis {Stuttard, 

 No. 42, 44, 45). Upper Lias, Stroud {Buckman). 



Observations. This elegant species is remarkable for the continual tapering through 

 its whole length, by which it happens that no part of the guard is really cylindroidal. 

 The angle of inclination of the sides of the phragmocone is very moderate (not exceeding 

 18° in the anterior part, but amounting to 24° in the hinder part); the section is 

 elliptical. 



In Mr. Moore's rich collection from Ilminster the growth of this species may be 

 traced with great satisfaction from an individual less than half an inch long to full-grown 

 examples of 6 and 8 inches from the apex of the guard to the last (or nearly the last) 

 chamber. Two varieties also appear of unequal proportions, one being much more 

 compressed, and with a longer guard. This is less common than the shorter variety. 

 The degree of distinctness of the furrows also varies, so that we may mark different 

 races ; the longer ones, indeed, may be (according to D'Orbigny) males, the shorter ones 

 females. 



Var. a. All the three furrows of the guard distinct, the ventral one usually longest. 

 j3. All the furrows indistinct. 



And to each of these the variations of length may be added. Striations can hardly be 

 traced about the apex, but occasionally appear in the ventral sulcus. 



Taken as a whole, it appears that this fossil more than any other resembles in shape 

 and proportions the original figvu'e given by Miller for B. elongatus ; but no specimen 

 corresponding to that figure has been found in the Bristol collection. On the other 

 hand, there are in that collection thick, tripartite Belemnites, with short axis of guard, 

 referred to B. elongatus of Sovverby, from the Upper Lias at Dundry, with an alveolar 

 angle of 25°. 



1 In one case this angle in the anterior part of the cone is found to be only 12°30' ; in another large 

 specimen, as much as 24° ; both exceptional instances. 



