AKTHEOPODA — . 



■AEACHNIDS. 



89 



not yet fused, and there are among the older fossils of this G-allery 

 Order many that show a similar or greater approach to the VIII. 

 Eurypterid plan. The first of these exhibited is tlie Silurian 

 Neolimidus, with at least nine free segments ; then Hemias'pis, Table-case 

 in which the last three are narrower than the others and are 

 followed by the telson. Belinurus from the Coal Measures 

 has eight abdominal segments, of which the last two or three 

 are fused ; while in the contemporaneous Euprodps [Prest- 

 icicliia] the segments are reduced to seven, and these are 

 fused. If the Coal Measure fossils known as Cyclus are not 

 larval stages of the contemporaneous Xiphosura, one can 

 only say that they are just what one Avould expect those 



Fig. 42.— a modern Xiphosure, Limulus polyphemus, the King-crab, a, 

 the upper surface ; 6, the under surface. About J^th the diameter of 

 the real animal. 



larvae to have been. The resemblance of all these early 

 Xiphosura to trilobites is also too striking to be overlooked. 

 Limuhcs itself first appears in the Trias ; several specimens Wall-ease 

 from the ^olenhofen stone of Kimmeridgian age are shown. 1^^- 



As the Eurypterida were assuming a fresh-water existence 

 before vanishing, the Order Scorpionida was making its 

 appearance, being first represented in the Silurian rocks by 

 what seems to have been an aquatic, if not actually a marine 

 form. This is Palaeophonus (Fig. 43), found in both Scotland 

 and Gotland. It consists of the same number of segments, 

 arranged in the same way as those of . Eurypterida, and 



