INVERTEBRATE PALAEONTOLOGY. 417 



advocated, with much ingenuity, an opinion first suggested by Scheuchzer, 

 thai they are the valves of a pedunculated Cirripedes, allied to Anatifa. 



The impression, however, has for some time been gaining ground among 

 palaeontologists thai these bodies really are organs or appendages of the 

 Cephalopoda, within the shells of which they are so frequently found ; and 

 since Darwin has shown that it is against all analogy to regard them as the 

 valves of Cirripedes, perhaps one of the most generally-received opinions lias 

 been that they are the opercula of Ammonites, Scaphites, Goniatites* &c. 



This latter opinion, however, is also controverted in the Upper Missouri 

 work cited above, in consequence of its incompatibility with peculiar struc- 

 ture of a very remarkable Trigonellites (= Aptychus), found in Scaphites 

 Cheyennensis, and described in connection with that species farther on. It 

 is also suggested there, without positively adopting this conclusion, that this 

 specimen favors Van Breda's opinion that these bodies are the oral apparatus 

 of Ammonites and other Cephalopoda, in which they occur. (See descrip- 

 tion of an Aptychus found in Scaphites Cheyennensis, at the end of the 

 description of that species.) 



Since these remarks were published, an entirely new view, originally 

 suggested by Professor Keferstein, in regard to the nature and functions of 

 these bodies, has been advocated by Dr. Zittel, Professor Waagen, and Pro- 

 fessor Favrc ; that is, that they were connected with an organ of these 

 ancient Cephalopoda, corresponding in position and functions to the nida- 

 mentary gland of the female Nautilus. Adopting this conclusion, Professor 

 "Waagen has proceeded to distribute certain types of the Ammonitidce into 

 groups and sections, based on the presence, absence, or peculiarities of these 

 bodies, as follows : 



A. Nidamentary gland without a solid integument (i. e., without an Apty- 



chus) : Phylloceras, Suess ; Lyttoceras, Suess ; Arcestes, 

 Suess ; Pinnoceras, Mojsisovics ; and Trachyceras, Laube. 



B. Nidamentary gland with a solid integument (*. e., with an Aptychus). 



I. Gland simple, not divided. 



i. Integument (aptychus) horny : Arie'ces, Waag. ; sEgoceras, 



Waag. ; Amaltheus, Montfort. 

 ii. Integument calcareous: Aptychus numida, Coq. (shell unknown). 



* Specimens of Trigonellites have been found in Devonian rocks associated with Goniatites. 

 53 H 



