CRUSTACEA. 



81 



No. 139. [1314, Cast]. Eusarchus scorpionis, Giote and Pitt. 



This member of the Eurypterida is regarded by the authors of the genus as 

 somewliat more specialized tliau the typical Eurypterus, as indicated by the 

 narrowness of the cephalothoracic portion and the abrupt constriction of the 

 posterior segments. The original is from the Water-lime group, Buffalo, N. Y. 



Size, 12 in. x 8 in. 



No. 140. [364, Cast), Limulus giganteus, Munst. 



This ancient " King-Crab," like those of the pres- 

 ent day, was covered by a cephalothorax shield; the 

 appendages were all oral ; and the eyes were sessile 

 and placed in the upper surface of the shield, while 

 the legs served the purpose of jaws and gills. It 

 doubtless lived along the shore of the ancient sea in 

 which were deposited the beds of lithographic lime- 

 stone (Middle Oolite), which are now worked at 

 Eichstadt, Bavaria, from which locality the original 

 of this fine specimen is derived. 



Size, 20 X 12. 



No. 141. [1316, Cast]. Euproops Danae, M. & W. 



This ancient King-Crab is interesting on account of its 

 resemblance to the larval form of the modern Limulus, 

 and still closer to the Carboniferous Trilobite Prestwichia. 



The original is from the Coal Measures of Grundy Co. , 

 111., and in possession of Ward & Howell. 



ORDER TRILOBITA. 



These extinct crustaceans were the earliest members of tlie 

 class, meetina; iis in the first formations in which we have any 

 abundant forms of marine life. Tliey resemble both the Ento- 

 mostracans and Isopods, and are nearly related to the JMerosto- 

 mata, Ijeing likened to the larvpe of the Horse-Shoe Crab. The 

 structure of the tero^al part only of their body is well known. 

 The longitudinal division into three lobes is not always distinct ; 

 but the head, thorax and abdomen (or tail) are generally well 



