298 Dr. H. Woochvard — The Position of the Merostomata. 



Pterygotus nasutus, Clarke. Frankfort Shale. 



P. prolificus, Clarke. ,, 



Stylonurus (?) limbatus, Clarke. ,, 



Megalograptus Welchi, Miller. Eichmond Group. 



Eurypterus prominens, Hall & Clarke. Clinton Beds. 



-B. sp. Arisaig, Nova Scotia. 



Drepanopteriis longicaiidatus, Clarke. Lockport Limestone. 



Euryptenis Boylei, Whiteaves. Elora, Ontario. 



E. Pittsfordensis, Sarle. Pittsford Shale. 



Stylomirus viultispinosiis, Clarke. Pittsford Shale. 



Hughmilleria socialis, var. robusta, Sarle. Pittsford Shale. 



Pterygotus Monroensis, Sarle. Pittsford Shale. 



Eusarcics cicerops, Clarke. Shawangunk Grit. 



Dolichopterus otisius, Clarke. ,, 



D. stylonuroides, Clarke. ,, 

 Stylonw-us cestrotus, Claxke. ,, 

 S. sp. a, sp. )8, sp. y. ,, 

 S. sp. 



Pterygotus globiceps, Clarke. ,, 



Eiirypterus lacustris, var. pachychirtis, Hall. Bertie Waterlime. 



E. pustulosus, Hall. Bertie Waterlime. 

 Dolichopterus siluriceps, Clarke. Bertie Waterlime. 



D. testudineus, Clarke. ,, 

 Pterygotus Cobbi, Hall. ,, 

 P. grandis (Pohlman). ,, 

 P. Atlantictis, Clarke. Devonic. 



P. sp. ,, Gaspe, Quebec. 



Euryptertis pulicao-is, Salter. ,, 



Eurypter ella ornata, M&tthevf. ,, New Brunswick. 



Stylonurus (?) Wrightiajuis (D&wson) . Portage Sandstone. 



S. Beecheri, Hall. Catskill Beds, Penn. 



Eurypterus approximatiis. Hall & Clarke. Waverly Beds. 



E. Mazouensis, Meek & Worthen. Coal-measures. 

 E. Mansfieldi, C. E. Hall. Coal-measures, Penn. 

 E. Pennsylvanicus, C. E. Hall. ,, 

 E.potens, C. E. Hall. 



E. stylus, J. Hall. ,, 



Since the important contributions made to this group by Professor 

 James Hall (1859-62) all zoologists have accepted tlie correctness of 

 his correlation oiLinmlus with Eurypterus, Pterygotus, and their allies. 

 But another question was raised by Sir E. Ray Lankester (in 1881) ' 

 as to whether Linmliis was indeed a true Crustacean after all, but 

 should be rather considered as an aquatic Arachnide. 



If we make a brief comparison of the characters of the three great 

 groups of Liraulidae, Eurypteridae, and Scorpionidse, we shall be struck 

 by the family resemblances they offer. 



In Limulus the body, although compressed, represents by its paired 

 appendages the concealed presence of a common number of coalesced 

 segments. The head-shield bears upon its upper surface both ocelli 

 and compound eyes. On the under side is the mouth with six pairs 

 of chelate appendages, the bases of which serve as mouth organs (save 

 the first pair) and for prehensile or walking-legs at their distal 

 extremities. The mid- and hind-body are coalesced and bear on the 

 under side six broadly expanded and united pairs of plates, the first 

 pair carrying the ovaries and genital pores, the five pairs following 



' " Limulus an Arachnid ? " : Quart. Journ. Micr. Sci., N.S., xxi, p. 609. 



