364. C. E. Beecher — Cambrian Eurypterid Remains. 



Art. XXXIX. — Discovery of Eurypterid Remains in the 

 Cambrian of Missouri / by C. E. Beecher. (With Plate 

 VII.) 



The wonderful development of merostomes in various parts 

 of the world at about the close of the Silurian has long been 

 recognized, and the suddenness of their appearance out of an 

 apparently clear paleozoic sky has been a matter of considera- 

 ble speculation. Almost at the same instant of time there 

 appeared on the geologic horizon a marvelous assemblage of 

 these ancient arthopods. A very few scattering forerunners 

 are known from older rocks, but most of them are small and 

 strange creatures, little resembling the characteristic Euryp- 

 terus and Pterygotus of the Upper Silurian, and in fact be- 

 longing to other orders of the Merostomata. 



In North America the known genera and species of the 

 order Eurypterida belong almost exclusively to the Waterlime 

 group (Rondout) above the Salina beds. Dr. John M. Clarke* 

 has recently announced the discovery, by Mr. C. J. Sarle, of a 

 new Eurypterid fauna at the base of the Salina, which carries 

 this peculiar biologic facies one comparatively brief stage fur- 

 ther back. Evidences of still older forms are very meager. 

 A single species of Eurypterus (E. prominens Hall) is referred 

 to the Clinton beds of the Silurian with considerable doubt. 

 The next indication of a greater antiquity of this order con- 

 sists of a fragment of an abdominal segment and a single 

 jointed limb, from the Utica slate of New York, described by 

 C. D. Walcottf as Eehinognathus Clevela?idi. 



It is therefore of considerable interest and importance that 

 a new and much older horizon for the Eurypterida can now be 

 chronicled. 



Mr. Arthur Thacher, President of the Central Lead 

 Company of Missouri, formerly a professor in Washing- 

 ton University, found a nearly entire specimen of a new 

 Eurypterid in the Potosi limestone of St. Francois county, 

 and through his generosity and the kindly interest of Mr. 

 Frank L. Nason, the specimen was transmitted to the Yale 

 University Museum. Owing to the supposed scarcity of fos- 

 sils in the Potosi and St. Joseph terranes of Missouri, their 

 correlation was long a matter of uncertainty, until Mr. Nason 

 described certain horizons bearing an abundant and character- 

 istic Cambrian fauna. 



* Notes on Paleozoic Crustaceans. N. Y. State Museum, Report of the State 

 Paleontologist for 1900. 1901. 



f Description of a New Genus of the Order Eurypterida from the Utica Slate, 

 This Journal (3), vol. xxiii, 1882. 



