MIDDLE LIAS FOSSILS. 189 
The Fauna of the Middle Lias is not by any means so rich as 
that of the Lower Lias. Vertebrate remains are but rarely found. 
Occasional bones of Ichthyosaurus and of Thaumatosaurus ( Ple- 
siosaurus) represent the Reptiles; and of Fishes we find only 
here and there remains of Hybodus and Lepidotus. Of Mollusca, 
the Ammonites include A. acutus, A. Engelhardti, A. Jimbriatus, 
A. margaritatus, and A. spinatus. Forms like A. Bechei, 
A. caprirornus, A. Loscombei, and A. striatus, characteristic of the 
higher beds of the Lower Lias have been recorded, but as will 
be seen, it is most difficult to draw any satisfactory plane of 
division between the strata of Lower and Middle Lias. Belem- 
nites are abundant, more especially in the Marlstone, and this 
division (including the Transition Bed) has yielded a large 
assemblage of Gasteropoda, belonging to the genera Act&onina, 
Cerithium, Chemnitzia, Cryptcenia, Discohelix, Pleurotomaria, 
Solarium, Trochus, and Turbo. Dentalium also occurs. Of 
Lamellibranchs we have a large series of genera including 
Area,, Arcomya, Astarte, Cardinia, Cardium (Protocardium), 
Cucullaa, Cypricardia, Goniomya, Gryphcea, Hi?initcs, Leda, Lima, 
Modiola y Nucula, Ostrea, Pecten, Pholadomya, Pinna, Pleuromya, 
Plicatula, Unicardium, &c. Brachiopoda are especially abundant 
in the Marlstone, and include Leptcena and Koninckella, Rhyn- 
chonella, Spiriferina, Terebratula, Waldheimia, and Thecideum. 
Crustacea, Polyzoa (rarely), and Annelides are likewise found 
in the Marlstone. Echinodermata as a rule are not abundant. 
Crinoidal fragments however enter largely into the composition 
of certain beds of Marlstone, and some of the hard beds of cal- 
careous sandstone in the lower strata yield Ophioderma, Tropid- 
aster and Uraster. Corals are represented by occasional species 
of Montlivaltia, Thamnastrcea, and Thecosmilia. Sponges liave 
been recorded, and many species of Foraminifera have been 
identified. 
The Flora is at present mainly indicated by the occurrence of 
undetermined " plant-remains " and lignite. 
MIDDLE LIAS FOSSILS. 
FIG. 54. 
FIG. 55. 
Ammonites margaritatus, Mont, f . 
