Geol.-Vol. I.] SMITH— PLACENTICER AS. 21 3 



been the ancestor of Ho-plites, this stage is called glyphio- 

 ceran, although Pro7iannites, or several other genera 

 excluded from this family by some writers, may have been 

 the parent group. In all probability this stage is pro- 

 siphonate, although the siphonal collars could not be seen 

 on any specimen, for the higher members of the Glyphio- 

 ceratid£e become prosiphonate with advancing age, and 

 many of the Cretaceous ammonites investigated become 

 prosiphonate almost as soon as they reach the goniatite 

 stage of development. 



At about one-quarter of the first revolution from the 

 protoconch, and at the fourth chamber-wall, a second 

 internal lateral lobe is added, something that no member 

 of the Glyphioceratidse is known to have possessed;^ this 

 stage is distinctly goniatitic, and yet not comparable to 

 any known genus, but is probably the result of unequal 

 acceleration of the septation, introducing elements that 

 belonged to later genera. This is shown on PL XXVII, 

 fig. 2, and illustrates the multiplication of the lobes by 

 the division of those inside the umbilicus, and gradual 

 pushing of these towards the ventral portion of the 

 shell. 



Parane^ionic. — At about five-eighths of a coil the new 

 internal lobe reaches the umbilical border, and the shell then 

 has two principal lateral lobes and one auxiliary. The larva 

 has then reached a stage correlative with the goniatites of the 

 Upper Carboniferous. This period of growth did not last 

 long, for shortly after the appearance of the constriction 

 which marks the end of the first coil the septa lose their 

 goniatitic character and become transitional to the 

 ammonite stage. This is shown on PI. XXVII, figs. 3 

 and 4, and the outside form of the shell on PI. XXIV, 

 figs. 6 and 7. At one and one-twelfth coils the shell is 

 transitional from the glyphioceran stage (Pronannites) to 

 what resembles closely the genus JVannites of the Trias, as 



1 Haug, "Etudes sur les GoniaUtes", p. 27, fig. 6, e, shows Pericyclus with two internal 

 lateral lobes, but this was wrongly copied from Holzapfel's original drawing, " Carbon- 

 Kalke von Erdbach", PI. Ill, fig. 6, where only one internal lateral lobe is shown. 



(3 ) August 8, 1900. 



