342 ARACHNIDA. XIPHOSURA 



free, and in some cases the abdomen is clearly separable 

 into mesosoma and metasoma 

 (fig. 146). In these respects the 

 Palaeozoic Xiphosura approach 

 both the Eurypterida and the 

 Scorpionida more nearly than 

 does Limulus. In most of the 

 Palaeozoic specimens the append- 

 ages are not preserved. The 



examples found in the Coal Fi 8- 146 - Semiaspis limu- 



loides, from the Lower 

 Measures may perhaps have lived Ludlow Beds. x£. 



in fresh water. 



Belinurus. Form similar to Limulus. Prosoma semicircular, 

 with a flat border and long spines from the posterior angles ; median 

 part raised, with compound eyes at the sides and median eyes at 

 the front. Mesosoma of five free segments, with the lateral parts 

 produced into spines. Metasoma small, formed of three fused seg- 

 ments with a long tail-spine. Coal Measures. Ex. B. regince. 



Prestwichia ( = Euproops). Prosoma similar to Belinurus. 

 Abdominal segments (probably seven) fused, with a flat marginal 

 part produced into spines, and a short tail-spine. Upper Devonian, 

 Coal Measures, and Permian. Ex. P. rotundata, Coal Measures. 



Hemiaspis (fig. 146). Prosoma semicircular, with spines at 

 the external margin and angles ; central part raised. Mesosoma of 

 six broad, short, free segments ; metasoma much narrower, of three 

 segments and a pointed tail-spine. Silurian. Ex. H. limuloides. 



Bunodes. Similar to Hemiaspis. Prosoma without spines. 

 Mesosoma with broad axial part. Metasoma of three or four seg- 

 ments. Silurian. Ex. B. lunula. 



Neolimulus. Prosoma very broad, rounded in front, with 

 spinose angles; with median eyes and compound lateral eyes. 

 Abdomen with eight or more free segments. Silurian. Ex. N. 

 falcatus. 



