33 



BELEMNITES OF THE LIAS. 



Belemnites acutus, Miller. PI. I, fig. 1. 



Reference. Belemnites acutus, Miller, * Geol. Trans.,' 2nd series, vol. ii, p. 60, pi. 



viii, fig. 9 (read April, 1823), 1826. 

 B. brevis, var. a, Blainville, ' Mem. sur les Belemnites,' p. 86, pi. iii, 



figs. 1, 1 a, 1827. 

 B. acutus, Sowerby, ' Min. Conch.,' p. 180, t. 590, fig. 7 (not fig. 10), 1828. 

 B. acutus, D'Orbigny, 'Terr. Jurass.,' p. 94, t. ix, figs. 8—14, 1842. 

 B. brevis primus, Quenstedt, ' Cephal.,' p. 395, t. xxiii, fig. 17, 1849. 



Guard. Conoidal, compressed, terminating in a sharp, nearly central point, some- 

 what drawn out ; on each side frequently a broad shallow groove, not reaching to the 

 point ; apex often striated, but not grooved. 



Transverse section oval, with flattened sides ; the ventral aspect broader than the 

 dorsal; axis a little excentric (PI. I, fig. 1, s"). 



Greatest length observed, 2'75 inches; greatest diameter, 0'66 ; axis, 100. 



Young specimens are longer in proportion, and very acute (PI. I, fig. 1, j). 



Brojwrtions. The normal diameter (y, d) at the apex of the phragmocone being taken 

 at 100, the ventral part of it is from 36 to 44, the dorsal 56 to 64; the shorter 

 diameter at the same point is 87 ; the axis of the guard 300. In young specimens the 

 axis is 400 or more. 



Phragmocone. Oblique, with excentric apex ; the sides are nearly straight, and 

 inclined at an angle of 27° or 28° \ the angle included between the dorsal and ventral 

 lines is about 32°. Section elliptical, as 100 to 91. Septa not observed, except near the 

 apex of the phragmocone. 



Varieties, a. Lateral grooves distinct (specimens figured). 



j3. Lateral grooves obsolete (not figured). 



Observations. The type specimens employed by Miller are unknown. There is in 

 the museum of the Bristol Institution a tablet marked B. acutus, Lower Lias, Cheltenham, 

 bearing two specimens. One, dark-gray in colour, corresponds to some of my specimens 

 from the same locality, presented to me by my much regretted friend H. E. Strickland, Esq. 

 The other, composed of yellow spar, fits well enough in figure to Miller's outline, but is 

 of a different species. The figure of this author is quite indeterminate, nor is Sowerby 's 

 sufficient for identification. But there is no reason for disturbing the common consent of 

 1 D'Orbigny gives the angles as 18° to 24°, probably a mistake. 



