194 INVERTEBRATE PALAEONTOLOGY 



stricted, range. Specimens showing the chitinous hooks 

 of the tentacles, and the " ink-bag " with its contents, 

 are not uncommon in the Lias and Oxford Clay. 

 Occasional representatives of the Sepioidea (Cuttle-fish) 

 have been found in the Lias and later strata. The first 

 of the Octopoda (Calais} occurs in the Upper Cretaceous 

 of Lebanon. 



(K) ARTHROPODA 



The Triassic period, though poor in Arthropod 

 remains, must have been a critical time in the evolution 

 of the phylum. Practically all the orders characteristic 

 of the Palaeozoic failed to survive the Permian, and 

 those of the Lias had a markedly modern aspect. 

 Mesozoic Crustacea were mostly Ostracoda, Cirripedia 

 and Malacostraca. The first-named group is excessively 

 abundant in many parts of the British Wealden, and 

 occurs in profusion in the Chalk, sometimes outnumber- 

 ing even the Foraminifera. Barnacles of such familiar 

 recent types as Pollicipes and Scalpellum were well 

 represented in Jurassic, and particularly Cretaceous, 

 deposits. Isopods (Wood-lice) are usually rare fossils, 

 but Archaeoniscus occurs in local swarms in the Purbeck 

 beds, especially in the Vale of Wardour. True Decapods 

 (Crabs and Lobsters) appeared first in the Trias. The 

 lithographic stone of Solenhofen (Upper Oolitic) contains 

 beautifully preserved specimens of Eryon ; the prawn- 

 like Glyphaea and crab Palaeocorystes (PI. xiv. fig. 10) 

 are not uncommon in the Stonesfield Slate and 

 Selbornian respectively. 



Arachnids, Myriopods and Insects are not well known 

 from British Mesozoic strata, although "beetle-cases "are 

 common in the Lias and Stonesfield Slate. Those insects 

 that occur seem referable to existing orders, showing in 

 this character a marked contrast from Palaeozoic types. 



