V. 



Recent Additions to our Knowledge of the 



Eurypterida. 



SINCE the publication of Dr. Henry Woodward's " Monograph of 

 the British Fossil Merostomata " in 1878 (3) the number of 

 important papers dealing with this group has been comparatively 

 small. The additions to our knowledge of the true structure of these 

 interesting Palaeozoic forms have, however, been of great value, and 

 their zoological affinities may be said to be fairly well established. 



The classical works of Huxley and Salter (1), Hall (2), and 

 Woodward demonstrated that the Eurypterids were Arthropods 

 whose body consisted of a carapace followed by twelve free segments 

 and terminating in a telson, the surface being more or less covered 

 with scale-like markings. The under surface of the carapace bore a 

 number of legs — five pairs, according to the above-cited authorities, 

 and it is in connection with these that some of the most important 

 additions to our knowledge have been made. These legs consist 

 typically of a basal joint, the inner margin of which is armed 

 with teeth and serves as a jaw, much as in Limulus or A pus. 

 At the posterior end of the tooth-bearing margin is attached (6) 

 a small oval epicoxite exactly similar to that found in the same place 

 in Limulus, and at the anterior angle is attached the long, usually six- 

 jointed ambulatory appendage. 



The last pair of legs is characterised in all members of the group, 

 except Stylonurus, by its greater size and usually somewhat flattened 

 form, and ends in an oval plate. This is usually termed the swimming 

 foot, but it seems more probable that it was used for anchoring the 

 animal firmly in the soft mud of the sea bottom, and possibly also for 

 shovelling up the sand and mud when the beast wished to conceal 

 itself. 



In Ptevygotus the most anterior pair of appendages are large pincers, 

 probably prehensile in function, and evidently attached in front of 

 the mouth, as jaw bases are wanting. They seem to have consisted 

 of only three long joints, though owing to the crumpling of the cuticle 

 of the proximal joint there is often an appearance of a greater 

 number. Behind the mouth there are — according to Schmidt (4) — 

 four pairs of ordinary walking legs, followed by the large " swimming 



