Nautilida. 



19 



cliambers, the last-formed of which is occupied by the body of the Aturia. 

 animal, the hinder ones successively deserted, being found, whilst ^'^J'^^^ 

 the animal is alive, to contain gas. A tube, or siphuncle, passes ^^ J^^^ 

 from the body-chamber through each septum of the shell. This la, Table- 

 siphuncle, which in the recent Nautilus is attached to the animal's *^*^® *®- 

 body, is a membranous tube, with a very thin pearly covering. 



Fig. 39. — Aturia aturi, Bast., from the Miocene (or Oligocene) of Dax, 



Bordeaux. 



A, front view of a specimen partly broken open, showing I, I, I, 

 orifices of the lateral lobes of the septa ; s, s, siphuncle. (Reduced 

 f nat. size.) 



B, side-view of A. aturi var. Australis, M'Coy, from the Miocene of 

 Victoria, Australia, showing the closed umbilicus and the fine lines 

 of growth. (Nat. size.) 



In the extinct genus Aturia the siphuncle is composed of a 

 succession of funnel-shaped tubes, each inserted into the preceding 

 one (Fig. 39). In others (Pig. 40) the siphuncle is beaded, while 

 in the oldest genera {Actinoceras, Gyroeeras, and Phragmoeeras) 

 the siphuncle is large, and contains in its centre a smaller- 

 tube with radiating plates between, like the lamellae of a coral 

 (Fig. 43). 



In some instances the siphuncle is preserved and the shell 

 destroyed, giving the appearance of a string of beads {Actinoceras) ; 

 or of a series of vertebrae of some higher animal {Huronia, Fig. 44). 

 Siphuncles of Suronia six feet in length and one and a half inches 



