440 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



" This third piece, as may be seen by reference to figures 3, j\ g, h, 

 differs entirely from any of the usual forms of Trigonellites or Aptychus, as 

 generally understood, and presents a very peculiar jaw-like appearance. It 

 consists of two rami joined together at their anterior end, and extending 

 backward so as to present, as viewed on either side, the form seen in figure 

 3, g, of plate 35; while figure 3, h, represents its inner side. 



" The presence of this third piece would seem to furnish another argu- 

 ment, if any were needed, against the conclusion that these fossils are the 

 valves of Cerripedes, since its form is such that it can scarcely be regarded 

 as homologous with any of the external shelly plates of those animals. Its 

 form, if not indeed its very existence, seems to be even more irreconcilable 

 with the somewhat generally-accepted opinion that these bodies are oper- 

 cula. It is not difficult to understand how the two valves might be opened 

 out, as in figure 3, i, and attached to a fleshy lobe, or some of the soft parts 

 of the animal, so as to perform the offices of an operculum ; but it seems 

 impossible to conceive how the third jaw-like piece could have been in any 

 way connected with an operculum. 



"In examining this curious third piece, one can scarcely fail to be im- 

 pressed with its resemblance to a jaw or beak. Indeed, so striking is this 

 analogy that I have been strongly inclined to adopt the conclusion that it is 

 such, notwithstanding the fact that this would seem to require that the two 

 enveloping valves should be viewed as forming together the opposing mandi- 

 ble, for which their form would seem to be badly adapted. The opinion 

 that these bodies may be jaws, instead of opercula — first suggested by von 

 Bidda, I believe — receives additional support from the entire absence, so far 

 as known, of anything else representing jaws or beaks within the thousands 

 of Ammonitoid shells that have been broken in various parts of the world; 

 while all of the known existing Cephalopods are found to be provided with 

 such oral organs. Again, it will be remembered that in the existing species 

 of Nautilus (the beaks of which are partly calcareous and partly corneous), 

 the upper mandible is received within and enveloped by the lower, much 

 as the third appendage here described lies between the two valves of our 

 specimen."* 



* I should explain here, that the figure 3, d, of this fossil ou our plate was drawn and arranged 

 mauy years back, when the periphery, or outer edge, of an Ammonite or other similar shell, was con- 

 sidered the dorsum ; consequently, that side of figure 3, <J, was placed upward, which really brings the 

 ventral side above, as the figure stands. • • 



