PLATE XX. 
Fig 
10. Terebratula Australis, : Quoy et Gaim. Perforate valve, twice the natural size. 
11. = == Imperforate valve of the same. 
12. am == Diagram of a longitudinal section (left half of the shell), 
representing the muscular system, &c., of the same. 
(The various structures in the three figures have the same 
reference letters.) 
A, Teeth or condyles. 
4, Dental sockets. 
C, Socket plates. 
D, Crural base. 
, Crura of the loop. 
ff, Loop. 
G, Dorsal median plate. 
Hf, Foramen. 
T, Deltidium (divided). 
J, Cardinal muscular fulcrum. 
a, Pedicle. 
, Superior pedicle muscles. 
ce, Cardinal muscles. 
d, Valvular muscles. 
e, Inferior pedicle muscles. 
SS 
J, Impressions of the posterior divisions of the 
valvular muscles. 
9g; Do. of the anterior divisions. 
