500 A. W. GRABATJ PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



genera and 158 species have been described; 14 genera or subgenera and 

 63 species of this number are recorded from North iimerica. 96 Consider- 

 ing the species so far described, it will be seen that the lithological char- 

 acters of the formations in which they are found, the numbers of repre- 

 sentatives, and the perfection of preservation are significant factors in 

 the interpretation of the conditions under which the Eurypterids lived. 



Pre-Cambric. — From the pre-Cambric 97 only one species, Beltina danai 

 Walcott, has been recorded. This occurs in the Grey son shales of the 

 Belt Terrane of Montana and the Altyn limestone of the same State ; also 

 in siliceous shales of about the same horizon in Alberta, Canada. Both 

 Walcott and Barrell consider the Belt formation non-marine, the beds 

 having been spread out by streams, and partly, perhaps, in fresh or brack- 

 ish waters, which were rarely in connection with marine waters. Walcott 

 thinks that Beltina, of which thousands of fragments have been found, 

 was swept in from the open ocean during one of the marine invasions, 

 but he also notes the possibility that this type may be related to some 

 fresh-water Branch iopoda. The main points, however, are that the frag- 

 ments are very numerous, that they occur in a non-marine or brackish 

 water formation, and that no typical marine organisms are found with 

 them. It should in this connection be stated that Clarke and Buedemann 

 question the merostome nature of the Greyson shale fossils, but admit 

 this for the specimens from the Altyn limestone and the equivalent beds 

 of Alberta, Canada. 



Cambric. — The Cambric and early Ordovicic are peculiarly wanting in 

 Eurypterid remains, and what few have been found have been confined 

 to North American formations. In the Middle Cambric there are un- 

 doubted marine Merostomata, discovered by Walcott in 1910 in the 

 Stephen shale in British Columbia, Canada. He found many wonder- 

 fully preserved specimens associated with trilobites and other marine 

 organisms, thus leaving no doubt as to the marine character of the for- 

 mation. Two genera are described, Sidneyia and Amiella, the former 

 from very perfect and abundant material, the latter from one broken 

 fragment. These "Limulava," as Walcott has classed them, would offer 

 a strong argument for the original marine habitat of the Eurypterids, 

 were they true Eurypterids. They are not, however, as is seen from a 

 comparison of the Limulava and Eurypterida, and Walcott himself has 



96 Memoir 14, N. Y. State Museum: The Eurypterida of New York. Beltina danai is 

 omitted from the list in this memoir, but is here added. 



97 Since these deposits are disconformably succeeded by Middle Cambric (sometimes 

 perhaps late Lower Cambric) marine beds, I see no reason why they could not be re- 

 garded as the continental equivalents of tne Lower Cambric marine strata of the regions 

 farther west— A. W. G. 



