TRILOBITA. 



371 



bita at present known to us. In Phillipsia (fig. 227) the 

 general form is like that of Proetus, but there are only nine 

 body-rings. The tail is semi-oval, distinctly segmented, and 

 with an " entire " margin ; and the eyes are 

 large, reticulated, and reniform. Griffithides 

 resembles Phillipsia in having nine body- 

 rings, but the glabella is pyriform, and is 

 destitute of lateral furrows, while the eyes 

 are small. 



9. LICHAD^. In this family we have only 

 the Silurian genus Lichas (fig. 2 2 8, D) in which 

 the head is very convex, and the frontal 

 grooves of the glabella are extended back- 

 wards, so as to enclose a central lobe. The 

 facial sutures are discontinuous, and the eyes 

 are small and smooth. There are eleven segments to the thorax, 

 with grooved pleurae; and the pygidium is larger than the head, 



Fig. 227. Phillip- 

 sia seminifem, of the 

 natural size. Car- 

 boniferous. 



Fig 228. A, Head-shield of A retlmsi )ia Konincld; B, Head-shield of Cyplutipis Bunneisteri ; 

 c, Head-shield of Proetiis Bohemicus; D, Head-shield and tail of Lichas palmatus; E, Head- 

 shield of Acidaspis Hcernesi. Silurian. (After Barrande.) 



and often presents prominent spinose ends to its component 

 rings. The crust is superficially more or less tuberculated. 



