THE TRILOBITA AND OTHER 

 ARTHROPODA 



i. Calymene blumenbachi (Fig. 55), the "Dudley 

 locust," is a familiar fossil, beautifully preserved in the 

 Silurian Limestone of Dudley in the Black Country, 

 formerly much worked as a flux for the iron-furnaces, 

 but now worked out. This was evidently an animal of 

 very different construction from those we have hitherto 

 considered. The main part of its body is seen to be 

 composed of a row of very short, broad divisions (somites, 

 or segments), thirteen in number, all alike except for a 

 slight diminution in size backwards. In front is a semi- 

 circular headpiece (cephalon), which shows suggestions of 

 somites like those behind ; and at the other end is a 

 tail-piece (Pygidium] showing very well-marked segmenta- 

 tion (division into somites). From end to end run two 

 nearly parallel grooves, which divide the whole body into 

 a median strongly-arched portion (mesotergum) and lateral 

 flatter portions (pleiiral regions). The existence of these 

 three portions of the body suggested the name Trilobita 

 for the group of fossils to which Calymene belongs. 



The trilobites are quite extinct and unknown outside 

 the Palaeozoic system. There are, however, abundant 



191 



