106 



From the peculiar form of the chambers and septa in this fossil, an 

 undulating or ibliaceous suture is formed, which necessarily approxi- 

 mates it to the genus Ammonites, and prevents our regarding any longer 

 this simple suture as one of the generic characters of Nautilus. 



The siphunculus in the recent nautilus, I believe, always passes 

 through nearly the middle of the septa. This is the case also with 

 those nautilites of Shepey, which bear the general form of N* pompilius ; 

 and with those found at Brentford, one of which, impregnated with 

 pyrites, is represented Plftte VII. Fig. 12. But in other specimens, as in 

 the one just noticed, it passes much nearer to the inner part of the shell. 

 In others, again, it passes nearer to the outer part of the shell ; and in 

 one specimen which I possess, from Yeovil, Plate VII. Fig. 16, it is seen 

 to run along the back of the shell. The septa, in these last specimens, 

 frequently have an undulating direction : the fossil approximating, both 

 in the situation of the siphuncle and form of the septa, to the Cornu 

 ammonis. 



It should be remarked, with respect to the size of the siphunculus, 

 that, independent of the difference which may perhaps take place in the 

 degree of dilatation of the tube, at the time of its becoming involved 

 in its matrix, considerable difference may result from the section of 

 a specimen by which the tube is displayed. Thus, if the longitudinal 

 section of the siphuncle is made directly along its middle, it will neces- 

 sarily display a wider opening than if the section had been made more 

 to either side. 



I am perfectly unacquainted with the nautilite without distinct cham- 

 bers, or visible concamerations, mentioned under the article nautilite, 

 by Bourguet, in his dictionary, on the authority of Spada, who describes 

 it : " Nautilites unius aufractus, dorso subrotundo, squameo, reliqua 

 corporis parte palmata." Spada, Cat. Lap. Agri Veron. p. 20. I am 

 also ignorant of the fossil which the inhabitants of Maltha call Capo di 

 gatto\ and which Lhwydd describes as Nautilita articulus, Lithoph. 



