1086 NEW YORK STATE MUSEUM 



interrupted by the accumulation of marl, and finally was closed 

 by another lime-forming interval, it is evident that the condi- 

 tions at these times were not favorable to the eurypterids. 

 These dolomitic limestones probably represent more open water, 

 or the temporary removal of some barlike barrier, and, probably, 

 a diminution in the salinity of the water. Though the fine char- 

 acter of the silt forming the black shale and the evidence of 

 interrupted sedimentation noted above, indicate slow accumula- 

 tion, the occupation by the eurypterids was apparently of 

 comparatively short duration, merely an incursion, as it were, 

 since the black shale all told does not exceed 2 feet in thickness. 



The fact that the eurypterids are often dismembered and 

 their parts distributed over considerable areas, and that a 

 dozen or more are frequently found side by side, with a com- 

 mon flexure, suggests that they may have been drifted up by 

 a current. On the other hand, the fine preservation of much 

 of the material, extending even to the delicate appendages, 

 shows that the currents were very weak, thus practically leav- 

 ing the animals in the position of death or molting. Their 

 grouping is very probably due also, in some degree, to their 

 gregarious habits or to their abundance. 



The tests of the eurypterids are black and carbonized. A line 

 of dehiscence around the anterior edge of the cephalothorax 

 indicates that in many cases these remains are mol tings. 



