yy 
from the Upper Greensand of Hunstanton. 177 
Mantell’s Plicatula spinosa, which is the young of P. inflata, is 
a very different shell. Woodward’s Plicatula sigillina is attached 
by the entire lower valve, and is of a different form. 
Spondylus gibbosus (D’Orb.). 
This may be described as an attached form of Lima obesa. 
In the early state the shell was attached, but afterwards became 
free. It is symmetrical, about two-thirds as wide as long. The 
upper valve is remarkable for a degree of inflation unusual in 
the genus, its height being equal to about half thelength. From 
the apex it expands in a wedge-form for three-fifths of its length, 
and then contracts semicircularly. The ribs are small, close, 
without spines, and seemingly one elevated and one depressed 
alternately ; but as the surface of the shell is not well preserved, 
this is not certain. Length 1 inch. It may be regarded as a 
variety of S. gibbosus (D’Orb.). The same shell occurs in the 
Cambridge Greensand. 
Ostrea vesicularis (Lam.). 
A small shell, quite flat, attached to a Perna. 
Ostrea curvirostris (Nills.). 
This shell differs a little from Upper-Chalk forms in being 
broader and less round posteriorly, but it is matched exactly with 
specimens from the Lowest Chalk of Burwell. 
Exogyra conica (D’Orb.). 
This is the shell figured in ‘ T. Crétacés,’ pl. 478. figs. 5-8. I 
fail to see the advantage of associating it with Sowerby’s shell. 
It is the fossil mentioned as #. conica in my list of Greensand 
Bivalves, and is not uncommon in the Cambridge Greensand. 
Exogyra Rauliniana (D’Orb.), var. arcula. 
This may be described as an Hxogyra with the mode of growth 
of Ostrea hippopodium. The shell is a broad ellipse, with the 
spire slightly coiled in, and the free valve increasing in growth 
at its base, the lines being curves, which extend from the apex 
round by the base for nearly half the circumference. The at- 
tached valve increases by a nearly equal amount of growth all 
round, and projects above the upper valve. Attached by the 
whole of the base. It wants both the ridging and folding of 
E. laciniata, and in the regular growth of the side resembles L. 
Rauliniana. Similar shells occur in the Cambridge Greensand, 
and differ from HK. Rauliniana sufficiently to make a distinct 
name a convenience. 
Ann. & Mag. N. Hist. Ser. 3. Vol. xvi. 12 
