AGES OF N^TUF.E. 



22U 



such, in particular, as those of the straight, chambered shells 

 called Ortl]occratites,some of which are twelve feet in length, 

 [OrtJioccras fusifor^me^ g.) There are also found some of a 

 coiled shape, like the Ammonites of the secondary age, but 

 having less complicated parhUons, (TrocJioIites (nmnonius^d.) 

 The true cuttle-fishes, which are the highest of the class, 

 are not yet found. On the contrary, the Biyozoa, which 

 have long been considered as polyps, but which, according 

 to all appearances, are mollusks of a very low order, are 

 very numerous in this epoch. 



476. Tiie Articulata of the Palceozoic age are mostly 

 Trilobites, animals which evidently belong to the lower 

 order of the Crustaceans, (Fig. 156.) There is an incom- 

 pleteness and want of development, in the form of theii 

 body, that strongly reminds us of the embryo among the 

 crabs. A great many genera have already been discovered. 



Fig. 156. 



We may consider as belonging to the more extraordinary 

 the forms here represented, {Harpes^ a ; Arges, b ; Brori" 

 ies, c; and Platynotus, d ;) the latter, as well as the Isotelus 

 the largest of all, being peculiar to the Palseozoic deposit of 

 this country. Some others seem more allied to the crusta« 

 eeans of the following ages, but are nevertheless of a very 

 extraordinary form, as Eurypterus remipes, (e.) There are 

 a so found, in the Devonian, some very large Entomostraca. 

 The class of Worms is represented only by a few Serpulse, 



