448 



MESOZOIC TIME. 



The Middle Purbeck has afforded relics of about fourteen species 

 of Mammals, along with fresh-water shells and Insects. The species 



Figs. 818, 819. 



Mammals. 



■ Fig. 818, Amphitherium (Thylacotherium) Broderipii (X 2); 819, Phascolotherium 

 Bucklandi (X 2). 



have been referred mostly to the Insectivorous Marsupials ; but two 

 species, of the genus Plagiaulax, have the teeth of Rodents, aud were 

 related to the Kangaroo-rat ; while another, of the genus Galastes, as- 

 large as a polecat, was a Predaceous Marsupial. The remains of the 

 Purbeck were all " obtained from an area less than 500 square yards 

 in extent, and from a single stratum but a few inches thick." 



Characteristic Species. 

 1. Liassic Epoch. (L. stands for Lower Lias, M. for Middle, and U. for Upper.) 



1. Radiates. — Polyp Corals. — Isastrcea Stricklandi Duncan, L.; Montlivaltia, 

 Guettardi Dfr., L. ; M. mucronata Dune, L. ; M. cuneataDunc, M. ; Thecocyathus rugo- 

 sus Dune, L. ; Thecosmilia Tarquemi Dune, L. (genera of corals widely different from 

 the Paleozoic); Crixoids, Pentacrinus Briareus Mill., L. ; P. ba salt if 'or mis -Mill., L. ; 

 Echlnoids, Fig. 773, Diadema seriate Ag.,L. ; Cidaris Edwardsii Wright, L. British 

 Liassic species of Holothuria have been made out, from the occurrence of minute wheel- 

 shaped calcareous pieces, such as are found in some sections of the tribe. 



2. Mollusks. — Brachiopods, Fig. 777, Spirifer Walcotti Sow., L., and M. ; 

 Terebratula numismalis Lam., L., and M. ; T. rimosa Buck, M. ; Rhynchonella acuta 

 Sow., L. ; Figs. 775, 776, Leptaena Moorei Dav., U. ; 776 a, natural size; P. variabilis 

 D'Orb., L. Five species of Leptama and about twice as mam- Spirifers occur in the 

 Lias. While these old Silurian genera were disappearing, the new Brachiopod genus 

 Thecidea began; and with it there were Lingidce, Rhynchonellce, and Crania, and many 

 Terebratula. The genera Rhynchonella and Crania, it should be remembered, are lines 

 reaching from the Silurian to the present time; and Terebratula dates back to the 

 Devonian. 



Lamellibranchs. — Fig. 779, Gryphaa incurva Sow., L. (Gryphite Limestone); 67. 

 gigantea Sow., M. ; G. cymbium Lam., M. ; Gervillia crassa Buckm., L. ; Ostrea liassica 

 Strickl., L. ; 0. Knorrii Voltz, U. ; Fig. 778, Lima (Plagiostoma) gigantea Sow., L. ; 

 Cardinia (Pachyodon) Listeri Stutch., L., and M. ; Pecten cequivalvis Sow., M. ; Phola- 

 domya ambigua Sow., U., M., and L. : Gasteropods, Pleurotomaria Anglica Dfr., L. ; 

 P. expansa Phill., L. and M. ; Turbo heliciformis Geol. Surv., L. ; T. subduplicatus 

 D'Orb., U. : Cephalopods, Fig. 788, 788 a, Ammonites Bucklandi Sow., Brngt., L. ; 



