BUFFALO SOCIETY OF NATURAL SCIENCES 1 5 



course of which he may find better preserved fragments in the Belt 

 terrane, leaving no doubt as to the nature of the organisms; or, he 

 may find other structural and stratigraphic evidence for the correla- 

 tion. "On the basis of lithologic characteristics," he says, "the 

 Altyn would be correlated with the Newland limestone, and the 

 Grinnell and i\ppekunny with the arenaceous series above the New- 

 land limestone." But he further points out that "In deposits of the 

 character of those of the Algonkian in Montana, lithologic character- 

 istics are really of very little value over extended areas, as most of 

 the calcareous formations are in the form of great lentils, and these 

 are not comparable with the calcareous deposits of the Palaeozoic." 



Cambric. In the Middle Cambric there are undoubted marine 

 Merostomata, discovered by Walcott in 1910 in the Stephen forma- 

 tion in British Columbia, Canada. He has described two genera, 

 Sidneyia and Amiella, referring them to the Eurypterida in the sub- 

 order Limulava. As will be shown later, these forms are not true 

 eurypterids, and need, therefore, no further mention here. 



The only unquestionable eurypterid from the Cambric is Beecher's 

 Strabops thacheri from the Potosi limestone at Flat River, St. Francois 

 county, Missouri (19, pi. VII). Of this species a single specimen 

 was found for which the genus was erected. It is a nearly complete 

 individual, the dorsal aspect of which is well shown, though none of 

 the appendages are visible. It occurs in a yellowish, argillaceous 

 calcilutyte from one of the lower members of the Potosi. The slab 

 upon which Strabops occurs contains no other organic remains, 2 

 but Beech er has described a collection made by Nason from these 

 same beds in which there is an abundant marine fauna consisting 

 of fragments of trilobites with a few brachipods and other forms 

 (Hyolithes and a small Platyceras) (20, 362, 363). It is to be 

 regretted that Beecher did not, or was not able to specify more exactly 

 the stratum in which he found the eurypterid, for the Potosi limestone 

 in the Flat River section is 350 feet thick, not counting the 106 feet 

 of slates and conglomerate below and another 100 above, all of Potosi 

 age, and of course, it is by no means certain that the marine fossils 

 occurred in the same bed with the eurypterid. In fact, so far as the 

 material is concerned, this seems not to have been the case. 



Ordovicic. From the Ordovicic until just recently only one 

 occurrence had been noted, that of Echinognathus clevelandi Walcott , 



2 The type of this species is in Yale University, but the counterpart of the type is in Columbia 

 University Paleontological Collection, specimen 18122. 



