138 
the right or left, a circumstance I have not observed in' 
other species ; the beak is so much incurved as almost to 
touch the upper valve, the internal appendages to the 
hinge appear to be short and obtuse, but I am not certain 
that I have seen them perfect. 
Not uncommon near Oxford in Clay, which is often 
sufficiently soft to be washed away and shew the inside 
of the valves, but in general very much broken. At 
Ringstead Bay and Weymouth Ferry it occurs more 
perfect, as I learn from specimens lent me by Professor 
Sedgwick and Mr. De la Beche. They are in Marl, 
sometimes indurated, which according to the Professor 
belongs to the Kimmeridge Clay formation. 
Fig. 3, represents a more depressed shell, found in 
Marie, at Gunton in Suffolk ; its inferior size, with the 
same disposition of its plaits, and equally incurved 
beak, lead me to think it is only the young of the 
T. inconstans. 
TEREBRATULA dimidiate 
TAB. CCLXXVII. —Fig. 5. 
Spec. Char. Transversely obovate, subdepressed, 
with a projecting beak, plaited ; upper valve 
convex ; plaits about 30, half of which, on 
one side, are elevated. 
B ear nearly straight, and the width greater than the 
length. These characters distinguish this from T. in- 
constans, fig. 4 ; the straight beak distinguishes it from 
fig- 3. 
This is a siliceous cast, in which the Calcedony has 
assumed the form of concentric rings. It is from 
II alldown. 
