88 



HISTORICAL PALEONTOLOGY. 



lived type. The LingidellcB and their successors, the LingulcB, 

 are singular in possessing a shell which is of a horny texture, 

 and contains but a small proportion of calcareous matter. In 

 the Upper Cambrian Rocks, the Z/;z^/^/<?//<^ become much more 

 abundant, the broad satchel - shaped species known as Z. 

 Davisii (lig. 32, e) being so abundant that one of the great 

 divisions of the Cambrian is termed the " Lingula Flags." 

 Here, also, we meet for tbe first time with examples of the 

 genus Orihis (fig. 32,7^ k^ I) a characteristic Palaeozoic type of 



Fig. 32. — Cambrian Fossils : a, Protospongia fenestrata, Menevian Group; h, Areni- 

 coUtes didyvius, Longmynd Group ; c, Lingjilella femigi^iea, Longmynd and Menevian, 

 enlarged; d, Hymenocaris verjuicanda, Lingula Flags; e, Li7igiilella Davisii^ Lingula 

 Flags ;y, Orthis lenticuiaris, Lingula Flags; g, Theca Davidii, Tremadoc Slates; h, 

 Modiolopsis Solverisis, Tremadoc Slates ; i, Obolella sagittalis, interior of valve, Mene- 

 vian ; y, Exterior of the same ; k, Orthis Hicksii, Menevian ; /, Cast of the same ; ni, 

 Olerius muntrtis, Lingula Flags. (Alter Salter, Hicks, and Davidson.) 



the Brachiopods, which is destined to undergo a vast extension 

 in later ages. 



Of the higher groups of the Mollusca the record is as yet 

 but scanty. In the Lower Cambrian, we have but the thin, 

 fragile, dagger - shaped shells of the free - swimming oceanic 

 Molluscs or '' Winged-snails " {Fkropoda), of which the most 

 characteristic is the genus T/ieca (fig. 7,2, g). In the Upper 

 Cambrian, in addition to these, we have a few Univalves 

 {Gasteropoda), and, thanks to the researches of Dr Hicks, 

 quite a small assemblage of Bivalves {Lamelhbra?ichiata), 

 though these are mostly of no great dimensions (fig. 32, h). 

 Of the chambered Cephalopoda (Cuttle-fishes and their aUies), 



