42 CARBONIFEROUS AMMONOIDS OF AMERICA. 



two or three parts by secondary sinuses. In addition to these there are 

 several aaxiHary lateral lobes, three to six, all slightly pointed, while all the 

 saddles are rounded. No constrictions or other surface ornamentations are 

 known, except that on the adult body chamber faint ribs have been observed. 



The first septum of Pronorites is latisellate, and the broad sinus is soon 

 divided by a siphonal lobe into two lateral sinuses (PI. XII, fig. 1). This is 

 the end of the embryonic stage, in which the sliell is seen to belong to an 

 ammonoid cephalopod, but the family is not yet indicated. 



In the next stage the lateral sinuses are subdivided b}" broad, rounded 

 lobes; the sutures then resemble those of Goniatltes (Ihergiceravy tetragonus 

 Roemer, and the shell is in the beginning of the larval or nepionic stage; a 

 little fui-ther on the sutures are like those of a Prolecanites (P. serpentinus 

 Pliillips), and the larval stage is approaching its end. 



In the following or neanic stage the siphonal lobe becomes three- 

 pointed, and the shell corresponds to Paraprolecanites Karpinsky, and its 

 family aihnities are beyond doubt (PI. XIII, fig. 5). 



Witli the adult or ephebic stage the first lateral lobe becomes divided 

 into two or three parts (PI.. XIII, fig. 5c-f). With this stage the genus 

 Pronorites stops; but Gemmellaro has described froan tlie Permian of Sicily 

 a further development of tins series in the genus Parapronorites, in which 

 the double lateral lobe and some of the simple ones become serrated. 



Another line of development of Pronorites has been described b}^ Gem- 

 mellaro as Slcaiiites, in which all the lateral lobes become double like the 

 first one. The next higher stages are given by Medlicotfia Waagen, in 

 which the siphonal saddles become indented and annnonitie. Karpinsky* 

 shows that Medlicotfia in its development goes through the Ihergiceras, 

 Prolecanites, Paraprolecanites, Pronorites, Sicanites and Promedlicottia stages. 



Pronorites is represented in America by two species, one hi the upper 

 part of the St. Louis-Chester stage, and one in the ^Middle Coal Pleasures, 

 both in Arkansas. The finding oi Pronorites in Arkansas is of great impor- 

 tance, since it is the ancestor of Medlicottia, which, though unknown in 

 Arkansas, has been found at no great distance away in the Texas Permian. 

 Pronorites, on the other hand, has not yet been found in Texas. 



" Holzapfel has recently tihowii in Die Cephalopoden des Domanik ini sudlichen Tiniau, p. 45, 

 that Ibtjrgicenis ietrarjonm Eoemer is merely a young stage of Prcmoritk cyclolohus Phillips, and came 

 from the Carboniferous limestone instead of from the Devonian strata of the Hartz. 



''Ammoneen der Artinsk-Stufe, p. 41. 



