368 M. E. Favre on some Works relating to 



mark (that is to say, nearer the siphonal side), the same as the 

 iiidaraentary gland in the Nautilus. This important line once 

 ascertained, M. Waagen deduces from it by analogy the position 

 of the adductor muscle, of which the trace is ideally represented 

 in the figure by a dotted line. 



Apertural appendages. — We owe to M. Suess a detailed 

 study of these appendages in various groups of Ammonites. 

 In the group of the Fimhriati the ventral side shows nothing 

 but a broad, short, and but slightly marked process, while the 

 dorsal margin presents a long appendage which spreads far 

 over the preceding turn. In the Amalthei, the Falciferi^ and 

 the Cristate^ the keel extends far beyond the anterior margin 

 of the chamber, in a long appendage which M. Suess regards 

 as destined to support and protect the naked part of the body 

 of the Ammonite, and in particular the excretory canal, in 

 those groups which are distinguished by the smallness of their 

 last chamber ; this appendage curves outwards in A. rostra- 

 tus'\^ and inwards in A. Larnherti\. In a great number 

 of Ammonites {Ornati, Coronati, Planulati, Flexuosi^ Tri- 

 marginati) the margins of the shell are produced into lateral 

 appendages or auricles of various shapes, which M. Suess 

 regards, as I have already stated, as the points of attachment 

 for the muscles. In the typical Planulati the discoidal part 

 and the stalk of these appendages are both well developed ; in 

 the Coronati the stalk is always short and the disk very 

 large §; in A. JasonW^ these two organs are more or less 

 confounded. The often hollow spiral line that we see in 

 many Ammonites [A. lunula, A. canal iculatus, A. hifrons, &c.) 

 is produced as far as this appendage ; it is nothing but the 

 trace left by the stalk, which gradually incorporates itself 

 with the shell in proportion as the latter grows, while the 

 discoidal part is very probably subjected to resorption. 



If these lateral processes did not serve as points of attachment 

 for the muscles, what could have been their use ? The margin 

 of the aperture of the Nautilus is also falciform ; it is so in a 

 more marked manner in some Clymeniw, and still more in Ortho- 

 ceras undalatum. This process serves in the Nautilus for the 

 protection of the head, and in particular of the eye. We may 

 therefore suppose, with much probability, that it fulfilled the 



* See A. Amaltheus and A. costatus, Quenstedt, .Jura, p. 162 and pi. 21, 

 figs, l-.j ; Cephalopoden, pi. .5. fig. 10 a ; A. aerpentinus, Pictet, Traite de 

 Paleont. pi. o.'5. fig. 2 ; A. cristatus and A. varians, D'Orbigny, Cephal. 

 cret. pis. 88 & 92. 



t Buviguier, Statistique geolog. de la Meuse, pi. 31. fig. 8. 



X Quenstedt, Jura, pi. 70. fig. 10. 



§ D'Orbigny, Cephal. .Turass. pi. 140. fig. 1, pis. 1.3.5 & 1.39. 



II D'Orbigny, Cephal. Jurass. pi. lo9. fig. 1. 



