inches in length; sculptured in somewhat file-like fashion 
and at the posterior end furnished with a dark brown, 
horny appendage. The creature bores into clay and soft 
rock with a rotary movement, and possesses long siphons, 
by means of which it draws up and expels the water re- 
quired for its sustenance. 
North and South Islands. Narrow Neck, Auckland 
Harbour; Mount Maunganui, 
PHOLADIDEA TRIDENS (pholeo, to burrow; tridens, 
a trident, three-pronged spear or fork). —A white or cream- 
coloured rock-borer, of an elongated pear shape, rounded 
and bulbous at the anterior end, tapering off and flattening 
towards the posterior end. ‘The shell is thin and fragile, 
with an oblique groove on each valve in front of which 
is a triangular area, furnished with rasp-like ribs. The 
posterior end is truncated or cut off abruptly and has, at- 
tached to it, a pair of curved calcareous plates, one to each 
valve; each plate strengthened by a shelly trident on the 
inner surface in high relief. The interior is white and 
shining, with an oblique rib corresponding to the groove 
on the outside. It is rather more than one inch in length, 
and not so common as the P. spathulata. 
Found in the northern parts of New Zealand. Narrow 
Neck, Auckland Harbour; Mount Maunganui (found in 
water-logged timber), 
BARNEA SIMILIS (same derivation as Barnacle, a 
corruption of pernaculum, dim. of perna, a shellfish; simi- 
lis, like). —This mollusc is known as the Piddock, a rock- 
boring bivalve, about two and a-half inches in length, very 
asymmetrical in shape, the anterior end being pointed. The 
sculpture consists of concentric raised ridges, which at the 
anterior end are crossed by ribs radiating from the hinge. 
These ribs at the point of crossing are furnished with short, 
hollow spines, and the shell is curled over the beaks, which 
are quite hidden. The posterior end of the valves taper to 
a rounded point. The shells are rather fragile, and are 
white where the epidermis is worn off; otherwise the col- 
our is light brown. The valves have a wide gape at the 
anterior end, giving free scope to the muscular foot which 
supplies the motive force for the rasping revolutions of 
the shell. There is a protoplax present, which is an acces- 
sory plate of a lancet shape curved and hinged to join the 
two valves at the anterior end, close to the umbones. It 
probably represents the lunule in other bivalves. On the 
ocean beach at Mount Maunganui, and southward of Motu- 
riki, are to be seen, occasionally, long rounded and worn 
113 
Plate XI 
No 19 
Plate XI 
No. 21 
Sea Shells | 
of New Zealand 
