AGES OF NATURE. 



193 



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

 called Orthoceratites, some of which are twelve feet in 

 length (Orthoceras fusiforme, g). There are also found 

 some of a coiled shape, like the Ammonites of the secondary 

 age, but having less complicated partitions ( Trocholites 

 ammonius, d). The true cuttle-fishes, which are the highest 

 of the class, are not yet found. On the contrary, the Bryo- 

 zoa, which have long been considered as polyps, but which, 

 according to all appearances, are mollusks of a very low 

 order, are veiy numerous in this epoch. 



476. The Articulata of the Paleozoic 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 their 

 body, that strongly reminds us of the embryo among the 

 crabs. A great many genera have already been discovered. 



tt 



d ^KYVV^^S-^ " I %3P e 



Fig. 156. 



We may consider as belonging to the more extraordinary, 

 the forms here represented, (Harpes, a ; Arges, 1) ; Brontes, 

 c ; and Platynotus, d] ; the latter, as well as the Isotelus, 

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

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

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

 extraordinary form, as Eurypterus remipes (e). There 

 are also found, in the Devonian, some very large Ento- 

 mostraca. The class of Worms is represented only by a 



17 



