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 

 Buckiandi (X 2). 



have been referred mostly to the Insectivorous Marsupials ; but two 

 species, of the genus Plagiaulax, have the teeth of Rodents, and 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 Strichlandi Duncan, L. ; Montlivaltia 

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

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

 the Paleozoic); Crinoids, Pentacrinus Briareus Mill., L. ; P. basaltiformis Mill., L. ; 

 Echinoios, 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. rirnosa Buck, M. ; Rhynchonella acuta 

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

 D'Orb., L. Five species of Leptaina and about twice as man}- Spirifers occur in the 

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

 Thecidea began; and with it there were Linguke, Rhynchonella}, and Cranice, and many 

 Terebratuhz. 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, Gryphcea incurva Sow., L. (Gryphite Limestone); G. 

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

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

 Cardinia (Pachyodon) Listeri Stutch., L., and M. ; Pecten wquivalvis 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 Buckiandi Sow., Brngt., L. ; 



