3l8 NEW YORK STATE MUSEUM 



n i t i f o r m e has been well depicted by Holm [/. c, p.6, 7] and that 

 of the endosiphosheaths by Bather. We therefore take the liberty 

 of quoting from both of these authors. 



The first of these (cameras) originated in this way: On one 

 side of the upper portion of the visceral sac a circular and almost 

 inclosed constriction was produced.. The fold of the mantle thus 

 formed deposited shell matter making an inclined wall and a 

 division of a part of the originally open initial chamber. The 

 resulting chamber was empty and formed the first air chamber. 

 The chamber is, thus, bounded by only one septum and in this 

 case lies behind the wall corresponding to the first septum in 

 Nautilus. It therefore corresponds to the initial chamber in that 

 genus. As it here has the same function as the other air cham- 

 bers, 1 have termed it the first air chamber, although in fact it is 

 a remnant of the open initial chamber. Moreover, the second 

 air chamber is probably formed in part from the anterior portion 

 of the initial chamber. The visceral sac of the animal was now*" 

 divided by a constriction into an anterior and posterior portion. . . 

 The anterior portion now forms the actual habitation chamber, but 

 the great visceral sac also fills the posterior portion. Holm 



This writer describes further how, by the formation of more 

 cameras, the siphonal cord of the animal originates, and con- 

 cludes : ''Hence the siphon of Endoceras belemniti- 

 forme must have had its origin in a differentiation of the 

 visceral sac." This differentiation of the visceral sac by the 

 formation of several cameras also took place in C. brainerdi 

 [see pi. 6, fig.3 and text fig. 17] and may be taken as denoting the 

 metanepionic stage. Whether the cameras were formed for the pur- 

 pose of supplying a hydrostatic apparatus to the ever heavier grow- 

 ing animal, as Holm assumes, or whether they served simply the 

 purpose of shutting off space no longer used within the conch 

 by the animal which now grew rapidly forward and expanded 

 laterally, is here immaterial.^ 



^The possibility of a different function of the cameras from that of 

 having been air chambers has been asserted by Jaekel [see Zeitschr. d. 

 deutsch. geol. Gesellsch. 1902. p. 67] and discussed by the writer in a 

 review of Jaekel's paper [Am. Geol. 1903. 31:199]. 



