Il6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Anane^ionic. As soon as the first air-chamber is formed 

 the animal has left the embryonic and begun the larval stage, 

 and then takes rank with the chambered nautiloids. The 

 suture at this stage consists of a very broad ventral saddle 

 with a pair of narrow lateral lobes. On PI. XIII, fig. i, 

 is shown this suture ; fig. 6 shows this and also the second 

 chamber-wall; figs. 9 and 10 show the ananepionic suture 

 with half a coil attached, PI. XV, fig. i, shows the. in- 

 itial suture along with the later ones. While this stage can- 

 not be compared to any particular genus, it corresponds to 

 some nautilian form of the Silurian. The ananepionic siphon 

 is about half-way between the dorsum and the venter, in 

 this character, too, agreeing with the nautiloids. Where 

 the siphon passes through the partition the wall is bent 

 backward in a cone and has a siphonal collar around the 

 tube. The surface is still smooth, no ornamentation of any 

 sort ever having been seen on early stages of ammonoids. 



Metanepionic. With the second larval substage the shell 

 becomes a true ammonoid; this begins with the second su- 

 ture, which takes on the ventral lobe of the goniatites. The 

 shell is smooth as before, and the whorl changes little in 

 shape, being still low, broad, and little embracing. The 

 sutures and shape correspond exactly to Anarcestes, the 

 primitive goniatite and radicle of the ammonoids. Ana?'- 

 cestes was named but not characterized by Mojsisovics,^ and 

 afterward defined by Hyatt- as containing forms with 

 smooth, broad, and low whorls, with semilunular cross- 

 section, deep umbilicus, and rather broad abdomen. Goti- 

 iatites subnautilinus Schlotheim, of the Middle Devonian, was 

 chosen as type of the genus, but most of the species occur 

 in the Lower Devonian, in the Hercynian beds, which were 

 formerly assigned to the Upper Silurian. 



Glyfhioceras incisiim shows the Anarcestes stage at the 

 second and third sutures, and resembles closely yl. latesepta- 

 tus Beyrich of the Lower Devonian. On PI. XIII, fig. 6, 

 is seen the transition from the ana- to the metanepionic; 



1 " Cephalopoden der Mediterrauen Trias-Provinz," p. 181. 

 2" Genera of Fossil Cephalopods," p. 309. 



