SHELLS OF THE LIAS. 
355 
podium (Fig. 365),allied to Cypricardia^i^ also characteristic 
of the upper part of the Lower Lias. In this formation occur 
Fig. 363. Fig. 364. 
a h 
Avicula incequivalvis, Sow. 
Lower Lias. 
Avicula cygni 2 Jes, Phil. Lower Lias, Gloucestershire 
and Yorkshire. 
a. Lower valve, h. Upper valve. 
also the Aviculas, Figs. 363 and 364. The Lias formation is 
also remarkable for being the newest of the secondary rocks 
in which brachiopoda of the genera Spirifer and Leptcena 
Fig. 365. Fig. 366. 
Hippopodium ponderosum, Sowerby. Leptcena Moorei, Dav. Upper Lias, 
i diameter. Lias, Cheltenham. Ilminster. 
(Figs. 366, 367) occur, although the former is slightly modi¬ 
fied in structure so as to constitute the subgenus Spiriferina, 
Davidson, and the Leptaena has dwindled to a shell smaller 
in size than a pea. No less than eight or nine species of 
Spiriferina are c n’iinerated by Mr. Davidson as belonging to 
the Lias. Palliobranchiate mollusca predominate greatly in 
