246 



THE HABITAT OF THE EUEYPTERIDA 



which may occur among fluviatile organisms, but are inexplicable for 

 marine forms. In the upper Niagaran in North America H. socialis 

 occurs by the hundred in the Pittsford shale and the closely related 

 H. shawangunk, which may be only the young of the former species, 

 occurs in the synchronous shales of the Shawangunk, but in no other 

 part of the world at that time, so far as we know, were there any 

 representatives of Hughmilleria. It appears that the genus origi- 



Fig. 26. Eurypierus lanceo- 



latus Salter. X 2- 



(After Woodw. 1878, p. 142, 



fig- 44) 



Fig. 27. Hughmilleria socialis Sarle 



Xi 

 (After CI. & R. 1912, pi. LIX, fig. 1) 



nated in the rivers of Appalachia. Curiously enough, in the Upper 

 Ludlow, that is, lower Upper Siluric, of Scotland, Eurypterus lanceo- 

 latus appears, showing a striking resemblance to Hughmilleria socialis. 

 The prolific Scottish fauna of the Wenlock has revealed no possible 

 ancestors for this distinctive Eurypterus (or Hughmilleria?) and one 

 naturally wonders how it arose. Since Hughmilleria was restricted in 

 occurrence in the Niagaran, any migrations which took place must 

 have been effected during the Salina period. The important Salina 



