252 SMITH. [Vol. XVI. 



on PI. B, Figs. I and 2, and the septa on PI. D, Fig. 4, 

 although the third lateral lobe is considerably exaggerated, on 

 account of a mistake in drawing. But even if the third lateral 

 lobe were entirely lacking the stage might still be referred to 

 Paralegoceras, according to the usage of Hyatt. Throughout 

 this, as in all preceding stages, each coil embraces about two- 

 fifths of the preceding. By reference to the table of stages of 

 growth, the widening umbilicus and flattening whorl may be 

 traced just as in the drawings of the successive stages. This 

 substage is short, lasting only half a coil, from diameter 2.15 

 mm. up to two and five-eighths whorls, diameter 2.70 mm. 



The decrease in relative size of the siphon in the larval stages 

 may be seen from the following figures : 



At the first septum the siphon is 48 per cent of height of the whorl. 



At one-quarter of a coil " " 35 " " 



" one-half " " " 32 " " 



" three-quarters " " " 25 " " 



" one and one-quarter coils " '• 24 " " 



" one and one-half " " '• 23 " " 



" one and three-quarters coils " " 22 " " 



" two coils " " 20 " »' 



" two and one-half coils " "17 " " 



Neanic or Adolescent. 



Ananeanic. — When an ammonite in its development has 

 taken on characters that the goniatites never had, it may be 

 said to have completed the larval stage and to have begun 

 the adolescent. At the end of the Paralegoceras stage, diame- 

 ter 2.70 mm., about the middle of the third whorl, the abdomen 

 becomes sharpened and somewhat higher, and a keel appears. 

 The smooth sides, simple goniatitic septa, and ventral keel all 

 remind one of the Triassic genus Styrites ^ Mojsisovics. This 

 stage is shown on PI. B, Figs. 3 and 4, diameter 3.10 mm., three 

 whorls, with the beginning of the keel at diameter 2.70 mm. ; 

 the septa are seen on PI. D, Fig. 4. 



1 " Das Gebirge um Hallstadt," Abhandl. k. k. Geol. Reichsanstalt, Wien, Bd. 

 vi, p. 264, 1893. T^^ ontogeny of this genus is not described here, and we do 

 not know that it really goes through the prelinminary development of the 

 Glyphioceratidae. 



