514 HISTORICAL PALEONTOLOGY. 



Annelides (Arenicolites, Histioderma, &c.) Besides these, the 

 Longmynd beds of Shropshire have yielded a supposed Trilo- 

 bite (Palceopyge), The green and purple slaty rocks of Wick- 

 low have yielded two species of the singular fossil Oldhamia 

 (fig. 27), which may be a Hydroid Zoophyte, but which is 

 more probably a calcareous sea-weed. Lastly, the " Fucoidal 

 Sandstone " of Sweden, besides the obscure remains which are 

 known as " fucoids," has yielded the remarkable fossil known 

 as Eophyton (fig. 378), which is most probably a plant, along 

 with a small Lingula, 



In the Upper Cambrian Rocks, fossils become tolerably 

 abundant, and belong to varied types. The most character- 

 istic forms are Trilobites, the characters of which are so 

 peculiar as to have gained them the name of " primordial," 

 applied also to the strata in which they are found. The 

 chief genera are Paradoxides (fig. 114), Conocephalus, Sao, 

 Conocoryphe, Ellipsocephalus, Microdiscus, Agnostus, &c. The 

 " Primordial Zone " of Bohemia has also yielded a few 

 Pteropods, Brachiopods, and Echinoderms. The Potsdam 

 Sandstone of North America contains various primordial 

 Trilobites (especially those of the genus Dikelocepha/us), Bra- 

 chiopods of the genera Obolus, Obolella, and Lingula, Gastero- 

 pods of the genera Pleurotomaria and Ophileta, Annelide-bur- 

 rows (Scolithus), and numerous so-called " fucoids." Lastly, 

 in the Potsdam Sandstone have been detected the earliest 

 footprints, if they may be so termed, which have been as yet 

 discovered These have been described under the names of 

 Protichnites and Climactichnites, and they have probably been 

 produced by large Crustaceans. 



The Lingula Flags of Britain owe their name to the occur- 

 rence in them of a large satchel-shaped Lingula (L. Davisii). 

 Trilobites of the genera Olenus, Agnostus, Paradoxides, &c., 

 occur, and remains of Phyllopodous Crustaceans (Hymeno- 

 caris) are by no means rare. 



The Skiddaw and Quebec groups, as already mentioned, 

 are in a doubtful position, and are often regarded as being 

 referable to the Lower Silurian. They are chiefly noticeable 

 for the great abundance of Graptolites which they have been 

 shown to contain. Many of these belong to genera which 

 pass up into the Silurian rocks (Didymograpsus, Diplograpsiis, 

 and Climacograpsus) ; but others belong to types which are 

 exclusively confined to this horizon, and which are remarkably 

 complex as compared with later forms. Amongst these may 

 be mentioned the genera Tetragrapsus (fig. 32), Dichograpsus 

 (fig. 33), Loganograpsus, and Phyllograpsus. 



