AMMONITES— ZOOLOGICAL, ETC. 



77 



shaped, grooved, interrupted, tuberculated or canaliculated, 

 which gives greater value to the different modifications of 

 this part, 



I have observed these old margins in the Ligati (A. lati- 

 dorsatus, Parandieri, Mayorianus, raresidcatus, subfascicu- 

 laris, ligatus, Cassida, Emerici, Royerianus, Belus) ; amongst 

 the Heterophylli {A. incertus, toriisulcatus, Guettardi^ Ca- 

 lypso, and amongst the Capricorni (A. inaqualicostatus, 

 subfimbriatus, Honnoratianus, Lepidus, Mathesoni, quadri- 

 sulcatus, striatisulcatus, Duvalianus.) We find them also 

 in some of the Ammonites of the Jurassic formation, but 

 only in a very small number. These remains of the ancient 

 traces of the margin, are inflected anteriorly, forming a sa- 

 lient point on the dorsal mesial line, the examination, of a 

 great number of specimens, has proved to me that they are 

 always accompanied by a rim which is thicker than the 

 neighbouring portions of the shell. 



Accidental apertures {bouches accident elles) which leave 

 no trace, are the most extraordinary ; they cause great em- 

 barrassment, where we endeavour to connect their presence 

 and the regular growth of the shell. Before expressing my 

 ideas on the subject, I will endeavour to describe them. 

 They consist of two series of forms ; in the first they pre- 

 sent a very strong thick rim, often oblique to the lines of 

 growth and the ribs, and curved outwardly, as we see in 

 A. Asterianus of the Cretaceous formation, and in a consi- 

 derable number of Ammonites from the Jurassic formation, 

 such as A, Bronyniartii, Gervilii, ^c, all having the back 

 round, and belonging to the group of the Coronarii. Their 

 second modification, still more at variance with the regular 

 growth of the species, is that which we remark, in the spe- 

 cies having transverse ribs, and a large tongue on each side of 

 the margin, as in A, Macilentus (see fig. 3, PI. 2.) of the Cre- 

 taceous rocks A, Brackenridgii and many others which I pos- 



