190 ANCEID&. 
the following cut). Each valve is somewhat of an oval 
form, the outer edge nearly straight, fitting the somewhat 
triangular deep impression on the underside of the head: 
the inner margin of each valve is strongly ciliated, and 
a) 
oe pee % 
along the middle of the disc are three thickened circular 
calcareous masses (apparently representing the ossified 
centres of the three joints, of which this portion is pro- 
bably composed). The somewhat pointed Apex of each 
of these valves is furnished with a minute joint, setose at 
its tip. These valves are attached near the posterior 
lateral angles of the head; they are ordinarily shut 
together, their inner margins overlapping each other, so 
as to form an under covering of the head. Within 
them arises a much smaller and more delicate pair of 
appendages (possibly homologous with the first pair of 
gnathopoda) (hk but marked f in the above figure), 
composed of a somewhat square basal piece, with its 

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