﻿564 



can be seen in Fig. 19, which is enlarged six diameters, as a black 

 spot at the junction of the sutures and is visible only under a mag- 

 nifier in the original. The other figures are also enlarged six di- 

 ameters. 



Fig. 19 also shows the first three sutures and the highly acceler- 

 ated development of the first suture which takes on immediately 

 the peculiar lobes and saddles of the generic group to which this 

 species belongs, and also the great depth of the apical chamber. 



Aturia zizac, Bronn. 



Loc, Dax, France, Tertiary. 

 PL xiii, Figs. 20-22. 



Figs. 20 and 21 give front and side views of the nepionic and 

 half of the neanic stages enlarged about ten times with the first four 

 sutures. 



This species has a globose apex similar to that of Morrissi and 

 the umbilical perforation is also minute. This and the closeness 

 of the coiling is shown and the subdorsan siphuncle are shown in 

 Fig. 22. I have restored the dorsal shell of the ananepionic sub- 

 stage in this specimen. The extraordinary depth of the apical 

 chamber, the lobate character of the suture of the first septum, and 

 the highly tachygenic (accelerated) development of all of the char- 

 acters of the apex are noticeable in this species as in Aturia Mor- 

 rissi. 



Scaphites. 



The phylogerontic forms known by this name are of interest in 

 this paper because of the invariably excentric retroversal character 

 of the living chamber and their obviously intermediate station be- 

 tween the more uncoiled phylogerontic genera and such phyloge- 

 rontic genera as Sphaeroceras and the like which are closer ap- 

 proximations to normal shells and are consequently persistently in- 

 volute at all stages of development. 



The figures of this genus, in consequence of the retroversal bend 

 of the living chamber, do not usually give any data, and although 

 the literature is so abundant I was forced to make what observa- 

 tions I could in finishing up this paper upon the materials immedi- 

 ately in hand. In one fine large specimen of Scaphites from 

 Mingusville, Mont., Coll. Bost. Soc. Nat. History, I was able to 

 excavate the dorsum and found the impressed zone retained even 



