DISTRIBUTION AND OCCURRENCE OF EURYPTERIDS 503 



The material found in the Normanskill beds is entirely fragmentary, 

 so much so that the generic references are only provisional ones (loc. cit., 

 page 413). These genera are Eurypterus, Eusarcus, Dolichopterus, Sty- 

 lonurus, one species each, and Pterygotus two species, one doubtfully 

 referred. Five of the six species described are new, but one, Pterygotus ? 

 nasutus, has also been described from the Schenectady beds. As a rule, 

 only carapaces are preserved, but several small specimens have a few 

 abdominal segments attached, and one retains a part of a walking leg. 

 Portions of swimming legs and a telson of what appears to be an Erre- 

 topterus and one of a Pterygotus also occur. 



Summary for pre-Siluric. — Summarizing the evidence for the nature 

 of the habitat of the Eurypterids in pre-Siluric time, it appears that, 

 aside from the occurrence in the Schenectady and Normanskill shales, the 

 evidence seems to be in favor of a habitat not typically marine. In the 

 Belt Terrane the Eurypterid remains are found in fresh or brackish water 

 deposits, showing that in their earliest appearance they were not marine, 

 as is often stated. It may be argued that they were swept in from the 

 open ocean, but if that were the case we may ask: Why are no other ma- 

 rine organisms found associated with the hundreds of Beltina fragments? 

 Moreover, they are found in the lower part of the Greyson shales (3,000 

 feet thick), which pass into sandstone and conglomerate, indicating a 

 retreat rather than an advance of the sea. 100 As for the Cambric occur- 

 rences, the fauna of the Stephen shale, while undoubtedly marine, must 

 be disregarded, since the forms are not true Eurypterids. The one speci- 

 men from the Potosi limestone offers no evidence for either marine or 

 non-marine habitat, since the origin of the particular beds in which this 

 specimen occurs is not known. Even if marine, this single occurrence 

 would argue rather against than for a marine habitat of the Cambric 

 Eurypterids. The single fragment found in the Utica shale oilers posi- 

 tive evidence against a marine habitat as the normal one. At Holland 

 Patent the fragile graptolites are perfectly preserved in the black Utica 

 shale and the trilobite Triarthrus becki is found, with even its delicate 

 appendages intact. Here we have an organism similar in its general 

 structure to the Eurypterids and protected by an exoskeleton identical 

 chemically with that of the Eurypterids, both being of ehitin. Why, then, 

 we may ask, if these marine forms are so perfectly preserved, should only 

 a single appendage of a Eurypterid be found? If this form were nourish- 

 ing in marine waters, why are its remains not found under these ideal 

 conditions for preservation? The same argument would apply to frag- 



100 The Aiiyti limestone shows no positive evidence of marine origin, a. w.<;. 



