REVIEWS. 



31 



constant in all stages of growth, or, in other words, constant in their law 

 of development." Therefore, arguing from the relation which always 

 exists between the beak and the position of the siphon, he states, that a 

 knowledge of the general form of the former is sufficient in itself, to 

 determine the division to which the Belemnite belongs. 



Next to the general form, he considers the symmetry and invariable 

 features of development. The width of the alveolus, he states to be 

 an excellent distinguishing mark. 



The characters of the beak are those next to be observed ; — in the 

 first place he ranks the termination of the edges of the cavity, and se- 

 condly, the forms of the region of the alveolus, which is constant both 

 in families and species. 



The ventral canal being a form resulting from the presence of an 

 organic structure in the animal, the features which accompany it also 

 furnish distinguishing characters, such as its depth, relative length, 

 form of termination, and the angle of the sides. 



The apicial line is also to be considered, as being straight or curved, 

 central or otherwise. 



Lastly, the posterior termination furnishes an excellent character, as 

 being more or less central, sudden, or acuminated. 



Whilst all parts of the beak furnish characters by which the species 

 may be recognised, their relative value being determined hj the part 

 nearest the organs essential to the life of the animal, M. Duval-Jouve 

 attributes a greater degree of value to the general bearing as a dis- 

 tinguishing mark. 



Upon these principles the Author of this work has classi- 

 fied the Belemnites, which occur in the cretaceous groups of 

 the environs of Castellane, of each of which he gives a 

 concise, yet comprehensive description; containing the 

 specific characters, their localities, &c. as also remarks on 

 mal-formed species or monstrosities. 



We should be transgressing our proposed limit, were we 

 to insert the descriptions given of the characters of the 

 families, groups, and species of the district, but in order to 

 give a correct statement, we have added a tabular view of 

 them from the work before us. 



