29 
MODIOLA. 
Gen. Car. Bivalve nearly transverse, equilateral 
shell; posterior side very short, beaks lying 
towards the short side; hinge without teeth ; 
a marginal linear groove to which the cartilage 
is fixed ; only one muscular impression. 
MODIOLA depressa. 
TAB. VIUl.—Three upper figures. 
Spec. Cuar. Much depressed, ovate, narrowing 
towards the posterior side; surface smooth. 
"Tus shell is about 2! times as broad as it is long, and 
thin, the margin even and very regularly curved, it is 
altogether very flat, but particularly so at the anterior side; 
the beaks are very slightly prominent, and are rounded. 
Lines of growth faint. External coat shining, pellucid, 
internal pearly. 
This is not very rare at Highgate in the nodules of 
Septarium, at nearly the top of the great clay stratum, or 
in the clay itself, but then difficult to preserve, being so 
extremely tender, that, as the clay shrinks in drying, the 
shells crack and scale off in pieces, else the appearance of 
an epidermis is almost to be recognized. The pearly 
iridescent lustre of the inner coat inspires the finder with 
ecstacy, on account of the riches in his possession, which 
are perhaps to be preserved only for a few hours. The 
upper figure is from a specimen on a rather hard sandy piece 
of a Septarium, on the under side of which are a pair of 
Solen affinis. In the specimen below, taken out of the clay, 
the outer coat is preserved. The small specimen in the 
middie of the plate is from a Septarium found near Whitby, 
it is much thickened by fibrous. Carbonate of Lime. 
