1N/8."] SHELLS OF CEPHALOPODS. 95/ 



extravagant for adoption. And yet, if the Ammonite was tetra- 

 branchiate like the Nautilus, no other conclusion could logically be 

 drawn. 



Accordingly, such view is formally repudiated by the experienced 

 zoologist Dr. J. E. Gray, in his paper "On the Animal of the 

 Spirula"'. "The examination," he writes, "of this animal confirms 

 me in the opinion which I expressed in the ' Synopsis of the British 

 Museum' (1840, p. 149), that the Ammonites, from their texture 

 and the small size of the last chamber, are internal shells and should 

 be arranged with the decapodous Cephalopoids, being chiefly dis- 

 tinguished from the Spirilla by the siphon being always on the dorsal 

 margin of the whorls and the septa foliated on the edge. I am 

 aware," he adds, "that this opinion is not in conformity with the ideas 

 of many zoologists and comparative anatomists ; for Mr. Owen, in the 

 last arrangement of these animals (Todd's Encyl. Comp. Anat.), though 

 he places the Spirulce with the Dibranckiate Cephalopods, places the 

 Ammonites with the Tetrabranchiate next to Nautilus" (p. 259). 



Before recapitulating the grounds on which it was inferred that the 

 Ammonitidce were external shells, I will, finally, cite the valuable 

 Memoirs of the Geological Survey of India, published under the 

 direction of the accomplished and lamented Superintendent of the 

 Survey, Thomas Oldham, LL.D., F.R.S., in which the sanction 

 given to the views of Gray and before-cited authors as to the aspects 

 of the shells of the Ammonites has mainly induced me to offer the 

 present elucidation of the grounds on which I still hold the contrary 

 opinion, viz., that the siphuncle in the Ammonitidce is " ventral " or 

 " margino-ventral," as it is in Spirula, but that it is " external" in the 

 one and " internal " in the other, through the reversed direction of the 

 spiral whorls. 



In the " Monograph of the Cretaceous Cephalopoda of Southern 

 India," the preparation of which was confided to the accomplished 

 naturalist F. Stoliczka, too early lost to science, he premises the 

 following characters of the AmmonitidcB : — 



"Animal not known: shell spiral, more or less involute with 

 numerous regularly (?) and gradually increasing whorls in the same 

 plane, many-chambered, the last or body-chamber extending generally 

 over about two thirds of the last whorl. The margins of the septa 

 are deeply divided into lobes and saddles, the first having their sub- 

 divisions always pointed, the latter more rounded. The dorsal lobe 

 is divided by a small saddle into two parts, corresponding to the 

 siphuncle : in the regular forms of Ammonites this is always placed 

 in the middle of the back ; the siphuncle is also similarly placed 

 inside the shell." 



It is to be observed, however, that the author associates the 

 AmmonitidcB in the same order "Tetrabranchiata" with the 

 Naidilidce ; and it would seem therefore that he entertained the 

 doubts originally expressed by Gray 2 and supported by Grant 3 as 



1 Annals and Magazine of Natural History, vol. xv. 1845. 



2 Phil. Trans. 1833, p. 774. 



3 My description and figures were called in question, with more detail, by 



