Clarke — Early Stages of Certaix Goxiatites. 



167 



Ornamentation. The fine elevated striae which appear over a large 

 portion of the protoconch are directly transverse in their course and maintain 

 this character throughout the first and second whorls. Though at first of equal 

 size there is a gradual assumption of disparity until in later whorls the 

 tendency to f asciculation becomes distinctly marked, eventuating in the mature 

 condition, in the formation of node-like bunches near the inner or dorsal 

 margin. 



Toward the close of the third volution, the striae begin to show a slight 

 retral or hyponomic curve at the middle of the broad venter, and in the course 

 of the fourth whorl this curve is very distinctly defined, the lines forming a 

 narrow flattened band on the whorl, its width being about one-fourth that of 

 the whorl itself. This band becomes, in later growth, relatively much broader 

 and less distinct, producing in the ephebic condition an obscure flattening of 

 the volution. 



Suture. The precise form of the earliest sutures has not been made out, 

 but they could not be much simpler in character than that of all later stages 

 in which this suture line is direct save for a 

 strong ventral lobe. The entire course of the 

 suture at the seventh volution is shown in the Figure 5 Anar03tttl plebeiformU . Tha 



annexed figure suture at the seventh Tolution. 



The following inferences with regard to the phylogenic status of Ana/r- 

 cestes plebeiformis appear to be fully justified : 



(a) The immense size of the protoconch when compared with that of 

 other ammonoids indicates a closer approach to the stock whence the Goniati- 

 tince have been derived. 



(&) The strong ornamentation of the protoconch has been, in other 

 species, regarded as evidence of an acceleration or earlier inheritance. Yet in 

 many later goniatites showing acceleration in various characters not alone is 

 the protoconch devoid of ornament but the entire nepionic shell is also 

 smooth (e. g. MaMic. Patterson/, Hall). 



(c) The course of the sutrure is highly primitive throughout the life of 

 the individual. 



(e/) The whorls have, in sectional outline, throughout their existence, the 

 character expressed in only the earliest condition of later goniatites. 



(e) Not until the growth of the shell is well toward completion is there 

 any apparent gain or loss of umbilication. The ephebic and final whorls show 

 a slight increase in overlap and consecpient loss of umbilication. 



