Geol.-Vol. I.] SMITH— GLYPHIOCERATID/E. II7 



figs. 9 and 10 show the transition from ananepionic (first 

 suture) to metanepionic (second and third sutures) ; figs. 

 II and 12 show the Anarcestes stage at the first and second 

 sutures visible on the whorl. The metanepionic sutures, 

 seen in projection on PL XV, figs. 2 and 3, consist of a 

 deep, rounded, ventral lobe, and a pair of broad, shallow, 

 lateral lobes. When the animal has progressed thus far in 

 its development it is a true goniatite, and the siphon has al- 

 ready turned to the outside of the whorl, or abdomen. On 

 PI. XV, fig. 12, are shown for comparison the sutures of A. 

 subnautiliniLs (after L. von Buch, Gesammelte Werke, Vol. 

 IV, p. 116, PL XI, fig. 9). 



Paranepionic. When the broad lateral lobes become in- 

 dented with a pair of lateral saddles, the sutures, the narrow 

 umbilicus, and the broad, low whorl all correspond to Tor- 

 noceras Hyatt, of the Middle and Upper Devonian. G. 

 incisum reaches this stage at the fourth suture, at a diam- 

 eter of about 0.68 mm., one-third of a whorl, and continues 

 in it for the fourth, fifth, and sixth sutures, up to a diameter 

 of 0.80 mm., and five-eighths of a whorl. PL XIII, figs. 9 

 and 10, shows the form at the Tornoceras stage, at one-half 

 a whorl, with the following dimensions: 



mm. 



Diameter 0.74 



Height last coil 0.38 



Height last coil from the protoconch 0.13 



Width of last whorl 0.77 



Involution o . 26 



Width of umbilicus o . 06 



On PL XIII, figs. II and 12, the Tornoceras stage shows 

 at the fourth, fifth, and sixth sutures. 



Neanic. When the ammonoid in its growth no longer 

 shows the characters of its distant ancestors, but has already 

 taken on those of its own family, it may be said to have left 

 the larval stage proper and to have begun its youth. The 

 ananeanic is then the beginning of the adolescent period. 

 G. incisum at the seventh suture, three-fourths of a whorl, 

 and diameter of 0.85 mm., changes its form markedly; the 

 two pairs of lateral lobes become more pronounced, and 



