JURASSIC PERIOD. 453 



Chalk, and one in the Lias. Solenhofen has afforded a number of 

 species. 



The Mammals of the Jurassic have been found in the Lower 

 Oolite at Stonesfield, and in the Upper Oolite in the Portland "dirt- 

 bed" of the Lower Purbeck. 



The relics from the Stonesfield slate are referred by Owen to 

 Marsupials. Fig. 741 represents the jawbone of the Amphitherium 

 (Thylacotherium) Proderipii, and fig. 742, the same of the Phasco- 

 lotheriwn Bucklandi, — each twice the size of nature. The form of 

 the latter jaw is like that in the Carnivorous Marsupials (especially 

 the Thyalacini). The former species, according to Owen, is most 

 nearly related to the Marsupial Insectivores. Two species of Am- 

 phitherium have been found at Stonesfield. 



The Portland "dirt-bed" has afforded relics of about fourteen 

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

 The species have been referred mostly to the Marsupials, and but 

 one or two to the Non-marsupial Insectivores. 



Characteristic Species. 

 1. Liassic Epoch. 



1. Radiates. — Pentacrinus Briareus, from the Middle Lias; Star-fish of 

 different types, including that of the 



Opluura. Fig. 694, Diadema seriale, Fig. 694. 



from the Lower Lias. Also species 

 of Cidaris and Hemicidaris. 



2. Mollusks.— (a.) Brachiopods. 

 — Fig. 695, Leptsena Jfoorei, from the 

 Upper Lias, interior of ventral valve, 

 enlarged; fig. 696, dorsal valve of 

 same; fig. 696 a, same, natural size; 

 fig. 697, Spirifer Walcotli, from the Echinodekm.— Diadema seriale. 

 Lower Lias. 



Five species of Leptne.no, and about twice as many Spirifers, occur in the Lias. 

 While these old Silurian genera are disappearing, the new Brachiopod genus 

 Thecidea begins, and with it there are a few Lingulee, Rhynchonellee, and Craniee, 

 and many Terebratulse. The genera Lingnla, Rhynchonella, and Crania, it should 

 be remembered, are lines reaching from the Silurian to the present time; and 

 Terebratula is another genus dating back to the Devonian. 



(b.) Conchifcrs. — Fig. 699, Gryphxa arcuata, especially characteristic of the 

 Lower Lias or Gryphite limestone; Gryphsea Cyntbium, of the Middle Lias; 

 Hippopodium ponderosum ; fig. 698, Ctenoides gigantea. Other genera are 

 Pholas, Anatina, Pholadomya, Leda, Cythcrea, etc. 



(c.) Gasteropoda. — The genera Pteroceras, Planorbis, Paludina, Melania, Nerita, 

 etc., are supposed to begin here. 



