Notices of Memoirs — Prof. Beecher — Eurijpterns in Cambrian. 561 



age in Madison County, a little further south. In the absence of 

 other evidence the diagnostic value of this brachiopod is very slight, 

 and it is impossible to say w^hether the Bonne Terre, or St. Joseph, 

 limestones and the La Motte sandstones represent Lower Cambrian 

 terranes or whether they with the Potosi all belong to the Middle 

 or Upper Cambrian. 



The important point of this correlation is that, upon palgeontological 

 evidence which has hitherto been largely wanting, an extensive area 

 and thickness of sedimentary rocks are definitely placed in the 

 Cambrian. 



IL — Discovery of Eurypterid Remains in the Cambrian of 

 Missouri. With an Illustration. By Prof. C E. Beecher. 



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 Palaeozoic sky has been a matter of considerable 

 speculation. Almost at the same instant of time there appeared on 

 the geologic horizon a marvellous assemblage of these ancient 

 arthropods. A very few scattering forerunners are known from 

 older rocks, but most of them are small and strange creatures, little 

 resembling the characteristic E'wrypierMS and Pterygotus of the Upper 

 Silurian, and in fact belonging to other orders than the Merostomata. 



In North America the known genera and species of the order 

 Eurypterida belong almost exclusively to the Waterlime group 

 (Eondout) 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 further back. Evidences 

 of still older forms are very meagre. 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 consists of a fragment of an abdominal segment and 

 a single jointed limb, from the Utica slate of New York, described 

 by C. D. Walcott - as Echinognatlms Clevelandi. 



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 "Washington University, found 

 a nearly entire specimen of a new Eurypterid in the Potosi limestone 

 of St. Frangois 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 

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



1 Notes on Paleozoic Crustaceans. N.Y. State Museum, Report ot the State 

 Paleontologist for 1 900 . 1901. 



2 Description of a new genus of the Order Eurypterida from the Utica Sla4;e. 

 Silliman's Journal (3), vol. xsiii, 1882. 



DECADE IV. VOL. VIII. NO. XII. 3G 



