THE MOLLUSCA—HEDLEY. 509 
The brachial valve is externally horse-shoe shaped, and has a 
slight median boss. Internally it has a straight hinge line, from 
beneath which and in the plane of the valve, projects a stout 
cardinal process, whose transverse vertical section would form an 
omega, hollow downwards. On either side of the cardinal process, 
and corresponding to the teeth of the lower valve, are two deep 
triangular impressions, the sockets. All the free edge of the 
upper valve is granulated. The frontal emargination gradually 
passes into a funnel directed backwards; here originates the 
median septum which tapers distally to an acicular point before 
the hinge. The ventral face of the septum is hollow, on the right 
and left of it are produced curled flanges with serrate edges. 
These edges vary much; in some, presumably old, individuals 
they project irregular jagged lobes into the cavity. 
Fig. 57. 
If this median septum be compared to the tongue, then the 
teeth of the human jaw would answer in position to the lateral 
lobes of the brachial lamelle. Their development varies much ; 
what I take to be a young stage is shown in my drawing. In 
other, presumedly aged examples, the ‘‘canines” and “ molars ” 
project as tusks sideways and downwards, while the “incisors ” 
coalesce and advance towards the hinge. The cavity of the 
valve, exclusive of the septum and lamelle, has the surface 
densely perforated. 
This species was attached in considerable numbers, horizontally, 
perpendicularly, or obliquely (Fig. 57) to loose sheets of dead coral 
which I pulled up by tangles in forty to eighty fathoms on the 
western slope of Funafuti. At first inspection I mistook them 
