88 



HISTORICAL PALEONTOLOGY. 



Paradoxldes. In the higher beds, the number both of genera 

 and species is largely increased ; and from the great compara- 

 tive abundance of individuals, the Trilobites have every right 

 to be considered as the most characteristic fossils of the Cam- 

 brian period, the more so as the Cambrian species belong to 

 peculiar types, which, for the most part, died out before the 

 commencement of the Silurian epoch. 



All the remaining Cambrian fossils which demand any notice 

 here are members of one or other division of the great class 

 of the Mollusca, or " Shell-fish " properly so called. In the 

 Lower Cambrian Rocks the Lamp-shells (Brachiopoda} are the 

 principal or sole representatives of the class, and appear chiefly 

 in three interesting and important types namely, Lingulella, 



Fig. 32. Cambrian Fossils: a, Protospongia fenestrata, Menevlan Group; 6, Areni- 

 colites didymus, Longmynd Group ; c, Lingulella ferruginea, Longmynd and Mene- 

 vian, enlarged; d, Hyntenocaria vermicauda, Lingula Flags; e. Lingulella Davisil, 

 Lingula Flags; /, Orthis lenlicularis, Lingula Flags; g, Theca Dctvidii, Tremadoc 

 Slates; h, Modiolopsis Solvensis, Tremadoc Slates; i, Obolclla sagittalis, interior of valve, 

 Menevian;.?', Exterior of the same; k, Orthis Hicksii, Menevian; /.Cast of the same; 

 m, Olenus micrurus, Lingula Flags. (After Salter, Hicks and Davidson. ) 



Discina, and Obolella. Of these the last (fig. 32, 7) is highly 

 characteristic of these ancient deposits ; whilst Discina is one 

 of those remarkable persistent types which, commencing at 

 this early period, has continued to be represented by varying 

 forms through all the intervening geological formations up to 

 the present day. . Lingulella (fig. 32, c), again, is closely allied 



