6^ 



BRITISH BELEMNITES. 



Belemnites tripartitus, SMotheim. PI. XI, fig. 28. 



Reference. Belemnites tripartitus, Schlotheim, ' Petref. Belem./ No. 6, p. 48, 

 1820. 



B. elongatus, D'Orbigny, ' Pal. Franc. Terr. Jur./ p. 90, pi. viii,fig. 11, 

 1842. 



B. digitalis tripartitus, Quenst., ' Cepli.,' p. 419, pi. xxvi, figs. 14, 31, 

 1849. 



B. trisulcosus, Simpson, 'Lias Fossils,' No. 14, p. 26, 1855. (Section 

 ovate.) 



B. incism, Simpson, 'Lias Fossils,' No. 15, p. 27, 1855. (Section 

 nearly circular.) 



Guard, Straight, elongate, cylindroidal ; sides more or less flattened, tapering in a 

 continuous curve in the post-alveolar region to a three-grooved apex, which is distinctly 

 striated on the dorsal aspect for half the length of the axis of the guard ; grooves deep, 

 ening toward the apex. 



Sections show the contour to be oval, with the sides rather flattened, the dorsal part 

 rather broadest, except toward the apex, where the contrary happens ; the axis excentric 

 and straight. 



Greatest length observed (behind the expansion of the alveolar cavity), 63 inches ; 

 greatest total length, 9 inches ; greatest diameter, 1 inch. 



Proportions. Taking the diameter, v d, at the apex of the phragmocone at 100, the 

 ventral radius is 37, the dorsal 63, the cross diameter 88, and the axis 550 to 600. 



Phragmocone. Not seen in my specimens. The section of the alveolus is very 

 slightly oval. 



Locality. In the Upper Lias of Saltwick {Phillips). In the Jet-rock, Saltwick 

 [Simpson). In the Middle Lias of Banbury [Stuttard, No. 87). 



Observations. In its young state this species is not certainly known, unless, as I 

 think not improbable, B. suhtenuis holds that place. Its very distinct, straight, narrow 

 grooves, continued to the apex, distinguish it from the other triglyphic Belemnites of 

 the Upper Lias of Yorkshire. Its nearest relative is a beautiful species which occurs 

 in the Upper Lias of Ilminster and other localities of the South of England. Neither 

 of those species has been found (as far as I have seen) at Lyme Regis. A specimen 

 in my jjosscssion shows, on the dorsal aspect near the apex, a short, very narrow groove, 

 which docs not reach the apex (see PI. XI, figs. 28 (/ and s"). In a younger specimen 

 the striae arc interrupted, as in fig. 28 a. 



