GONIATITES. 



75 



ces.sfully l)rokcn out in condition to tioui'p, hut the imperfect ones obtained .showed 

 a gradual narrowing of the umbilicus and increa.se in height of the whorl and 

 involution. 



ADULT STAGE. 



The form of the adult G. cnnixtrid has already l)een sufficiently described in 

 this paper and in Hyatt's monograph. The sutures changed in increasing depth of 

 the ventral sinus and sharpening of tlu- lateral lobe.s, as shown on PI. XVI, lig. 1, 

 taken from a specimen of diameter of 15 mm. The early adult sutures have been 

 figured by Hyatt." and the figures are reproduced in this paper. 



PI. XV, fig. 9, shows a small specimen in the early adult stage; it agrees in all 

 essentials with those of larger growth, only the ventral saddle is shorter and the 

 lateral saddles more rounded. 



Tahla of stages of grovth. 



SUBIMART. 



The ontogeny of Goniatites is of interest not only for its own .sake, but also 

 because it is the most important genus of the largest family of ammonoids of the 

 Carboniferous, and because this famil}' gave rise to a large part of the ammonites 

 of the Trias. Goniatites in its ontogenv goes through the following stages: phylem- 

 bryonic, protoconch, representing the primitive cephalopod; ananepionic, Silurian 



"Fourth Ann. Rept. Geol. Surv. Texas. I'I, XLVII. tigs. Ai-i^. 



