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from its being exactly confined to the internal surface, I conceive that 
it belongs to the original structure of the shell. 
On clearing the larger valve, a reddish hue became very evident, and 
appeared to be the remains of the original colour of the shell. 
When the straight hinge and box-like form of this shell is considered, 
some resemblance will appear between it and the fossils which we have 
just been examining. But a more material coincidence is discoverable 
in the strong resemblance which exists between the surface of the back 
of the larger valve and that of the larger valve of the preceding fossil, 
Plate XVI. Fig. Vj , both surfaces being remarkably smooth, and formed 
by extremely fine transverse striae. 
CLIV. Hyalcea. A regular, inequivalved, transparent bivalve shell , 
gaping beneath the beak, tricuspidated at the base. 
This shell was originally described by Forskal, and named by him 
Anomia tridentata, and as such admitted by Gmelin. Lamarck has very 
properly placed it in a distinct genus. It is not known in a fossil state. 
CLV. Orhicula. A very small orbicular, flat bivalve. The lower 
valve very thin, and adherent to other bodies. The hinge unknown. 
This shell, only described by Muller, and named by him Patella 
anomola, is not known as a fossil. 
CLVI. Lingula. A long flat shell, composed of two valves, nearly 
equal, truncated anteriorly ; the hinge without teeth : the base or beak 
of the valves pointed, and united to a tendinous tube, serving for a 
ligament of attachment. 
Linnaeus, who had seen but one valve of this shell, named it Patella 
unguis. Bruguiere ascertained the nature of the shell, and assigned to 
it this genus. It has not been yet noticed as a fossil. 
In consequence of the similarity of the animals which inhabit the shells 
forming the two following genera, Linnaeus disposed them under one 
genus, which he named Lepas. But Bruguiere and Lamarck have, with 
