790 



THE WONDERS OF GEOLOGY. 



Lect. VIII. 



One of the most common species of Trilobite is that 

 known as the Dudley fossil Locust, and which has long 

 attracted the attention of collectors ;* this crustacean is 

 found either attached by the under surface to the rock, as 

 in Lign. 178, or coiled up like an Oniscus, or wood-louse.f 

 The Trilobites vary exceedingly in form and magnitude ; 

 some species not exceeding a few lines, while others are 

 eighteen or twenty inches in length. Some kinds, as the 

 Calymene, could coil themselves into a ball like the mille- 

 pedes ; while others had the central segments alone move- 

 able, as in Asaphus (Lign, 179) ; and many have a tail, or 

 post-abdomen (Lign. 180). In some species this tail is 



Lign. 179.— Tuberculated Trilobite, 

 from Dudley. 



Lign. 180. — Asaphus caudatus, 

 from Dudley. 



{Asaphusl tuborculatus.) 



a styliform process, as in the recent Limulus, and thrice as 

 long as the body. In the Silurian limestones of North 

 America, a gigantic trilobite, named Isotelus, from both 

 extremities of the body having a similar contour, is often 



* This Trilobite was figured and described by Lhwyd, in 1698. 

 f Medals of Creation, p. 553, fig. 4. 

 X Asaphus, signifying obscure. 



