200 OUR COMMON BRITISH FOSSILS. 



were free at their ends. The Calymenidce had cara- 

 paces roughened over with granules or tubercles, and 

 the number of body-rings was usually thirteen. In 

 HomalonotuSy one of the two genera composing this 

 family, the body-rings are not so distinctly trilobed as 

 usual. PhacopidcB was a family of Trilobites with 

 large facetted eyes. The number of body-rings is 

 eleven. The Lichadce had small head-shields, and a 

 tail or pygidium with a broad limb. It contains only 

 the genus Lichas. The Prcetida includes the Carbo- 

 niferous genera Phillip sia and Griffithsides. Their 

 number of body-rings was usually nine. The carapace 

 of Phillipsia is generally roughened with granules. 

 Acidaspidce had a very ornamental carapace, with 

 eight to ten body-rings, and the segments of the side 

 lobes (pleurae) directed backwards. The tail had also 

 two or three segments, furnished with prominent 

 spines. The Bronteidcs had a large expanded tail or 

 pygidium. The Harpeidcs were noted for the horse- 

 shoe-shaped head-shield, whose angles were greatly 

 prolonged. The body was numerously jointed, usually 

 with twenty-six segments. Only one genus, Harpes, 

 belongs to it. Lastly, we have the Cyphaspidce, whose 

 head-shield was also prolonged into spines, and the 

 carapace marked by spiny or pitted surface ornamenta- 

 tions. The number of body-rings varied in the 

 different genera from ten to twenty- two. These are 

 among the less common of the Trilobites. 



I have given the principal place to Trilobites 



