BELEMNITES OE THE LIAS. 47 



Belemnites paxillosus, Schlotheim. PI. VI, fig. 15. 



Reference. Belemnites paxillosus, in part, Schlotheim, 'Taschenb.,' pp. 51and70, 1813. 

 „ „ Voltz, 'Belemnites,' p. 50, pi. vi, fig. 2, and 



pi. vii, fig. 2, 1830. 

 „ „ Zieten,'Wurtemb.,'p.29,pl.xxiii,fig.l,1830. 



JB. Bruguierianus, D'Orb., 'Pal. Er. Terr. Jurass.,' p. 84, t. vii, figs. 1 — 5. 

 The plate is really numbered pi. vi, and the name on it is Belemnites 

 niger, also given on pi. v to another species. 1842. 

 .5.jO(3;a?e7/o5a*fl:»2«/^/ie«,Quenstedt,'Cephal.,'p.402,pl. xxiv, 1, 2, 4 — 8, 1849. 

 B. paxillosus, Oppel, 'Jura,' p. 152, 1856. 



Guard. Smooth, elongate, cylindroidal, convexo-conical towards the summit, which 

 is often subtruncate or even concave, and marked by two short latero-dorsal smooth 

 furrows, and in most cases by one or more medio-dorsal striae, and sometimes one medio- 

 ventral short stria. 



Sections show the axis to be nearly straight in all the young forms, only bending near 

 the apex in the older examples. The axis is a little excentric. 



Greatest length of axis, 3^ inches, and of whole guard, 65 inches ; diameter at apex of 

 alveolus not exceeding 1 inch. 



The young have nearly the same general figure and proportions as the adult indi- 

 viduals, and exhibit the same diversities as to compression, and sometimes assume a 

 subhastate shape. In very young forms the proportion of the axis of the guard is found 

 to be somewhat less than in those of middle age. Thus in a specimen from Wurtem- 

 burg the proportion in the youngest guards is 260, but in the same full-grown 

 individual 380. 



Proportions. The diameter [v d) at the apex being 100, the ventral radius is 40 to 

 45, the dorsal 55 to 60, the axis about 350 to 450. 



Phragmocone. Straight (or very nearly so), with a nearly circular section, the sides 

 meeting at an angle of 22° to 24°; conotheca distinctly striated, the straight striae 

 bifurcate toward the ventral region (Voltz) ; chambers rather shallow, numerous, their septa 

 almost directly transverse. (See figures of great value in Voltz, pi. vii, fig. 2.) The 

 depth of the chambers is one seventh of their diameter. The axis ends in a spherule. 



In a specimen from Ilminster the septa are traced in section through a length on the 

 axis of the phragmocone equal to half that of the axis of the guard. These septa are to 

 be coimted to above 60 in a space of \\ inch, the anterior septa being broken ofi" from 

 their flanged extremities, and lost ; the flanged extremities remain on the ventral side. 

 Broken septa occur within others which are not broken. 



