640 W. D. SMITH . 



ONTOGENY AND PHYLOGENY 



Scaphites nodosus var. brevis 



Ontogeny.— -This particular species or variety has been selected 

 on account of its typical development, and because of the amount 

 of material from which young stages could be worked out. 



According to Logan, 1 Scaphites nodosus goes through the follow- 

 ing stages in arriving at maturity: 



1. Anarcestes. 



2. Tornoceras. 



3. Glyphioceras. 



4. Gastrioceras. 



5. Paralegoceras. 



6. Pronorites. 



In Fig. 3, the writer has placed, for purposes of comparison, some 

 drawings of the sutures of typical species from the above-mentioned 

 genera. Beyond a. rather general similarity to Glyphioceras, the 

 writer can see no reasons for correlations. It would be seen, too, 

 from Branco's 2 excellent work on the young stages of ammonites, 

 that many ammonites, and especially of the Jura and Cretaceous, 

 have a Glyphioceran type of suture. It is thought by some that this 

 does not mean kinship with Glyphioceras at all, but that it is a 

 character acquired later, and pushed back by inheritance and accel- 

 eration until it is now found in the larva. In support of this, Professor 

 J. P. Smith cites the development of Pronorites that possesses a 

 Glyphioceran type of suture in its early stages of development, but 

 which is clearly known not to have come through Glyphioceras 

 at all. 



In Logan's paper the suture is made the sole basis upon which 

 relationships are based, and this lends itself to much criticism. As 

 Professor Smith and the late Alpheus Hyatt have both respectively 

 claimed, the suture cannot be taken as the sole criterion. Size of 

 whorl, shape of whorl, ornamentation, etc., must be taken into 

 account. 



Numbers 9 to n, Fig. 1, show the protoconch of this species. It 

 is not, in essentials, very much unlike the protoconchs' of many 



1 Logan, loc. oil., p. 210. • 



2 Branco, Entwickelungsgeschichte der fossilen Cephalapoden. 



