BELEMNITES OF THE CORALLINE OOLITE, ETC. 



iavtlicr along the ])hragmocone, 11 inches; the greatest diameter before the conical 

 expansion of the sheath over the phragmocone 1| inch. The smallest which has occurred 

 to me is little more than 1 inch long. 



Proportions in full-sized specimens. Taking the dorso-vcntral diameter at the alveolar 

 apex at 100, the transverse diameter is about equal to it, the ventral radius is 32, the 

 dorsal 08, the axis 250, justifying Miller's title of ^. «^(^rm«?'w.s. Li young specimens 

 the axis = 300. Cross sections near the apex show a still greater excentricity, the axis 

 curving towards the ventral surface. 



Phragmocone. Conical, a little incurved towards the ventral line, with an almost 

 perfectly circular section ; sides inclined at an angle of 18°, except near the apex, where 

 it is greater (above 20°). The septa are numerous, lie at right angles to the axis, with 

 plain imwaved edges, and are penetrated by a marginal siphuncle. 



Localiiy. In the Coralline Oolite and Calcareous Grit of Yorkshire at Malton, Scar- 

 borough, &c. In the same strata at Heddington, Cowley, Bullington, &c., near Oxford ; 

 near Calne, Weymouth, &c. In France, at Vaches-Noires and Marquise in Oxford Clay. 

 D'Orbigny quotes it from near Moscow. In Oxford Clay, Cowley, near Oxford. In 

 Kinmieridge Clay, Shotover. 



Varieties. In progress from youth to age, this Belemnite experiences considerable 

 changes, as may be inferred from what has been said in respect of the guard. Besides 

 these ordinary changes of form and proportion, it appears desirable to distinguish two 

 types of general shape, which occur in large specimens in some degree of relationship to 

 the stages of the strata. 



a. Belemxites abbreviatus (oxyruynchus). 



Large, cijlindroidal, slightly bent, with incurved, produced, flattened apex. Viewed 

 on the front or back, the sides are seen to contract rather suddenly from a cylindroid 

 part to the apex in the architectural form knowm as ogee (fig. 84, 0) ; viewed sideways, the 

 dorsal outline is continued in a convex form to or nearly to the apex, while the ventral 

 outline becomes concave under the apex (PI. XXXIV, fig. 84, /')• 



Locality. The Coralline Oolite of Malton, Oxford, and Wilts. An abnormal specimeif, 

 which places these characters in a strong light, is presented (PI. XXXV, fig. SO) from 

 near Oxford. 



/3. Bl'.LEMNITES ABBREVIATUS (EXCENTRICUS). 



Large, conoidal, with sides almost straight, converging through the whole post-alveolar 



19 



