22 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
Amphithyris buckmani sp. nov. 
(Plate XV, fig. 29; plate XVI, fig. 35) 
Habitat. —With Liothyrdla neozelanica on a stone entangled on a fishing line of 
200 fathoms length, Cook Strait, off Wellington, New Zealand. 
The shell is broadly sub-orbicular or roundly sub-rectangular, with an obtusely 
angled beak and a broad, nearly straight hinge-line, the greatest breadth being about 
the middle of the shell. The ventral valve is feebly convex, and the dorsal valve nearly 
flat, the commissures being straight. The beak ridges are sharp, and meet in an obtuse 
apex, which has not been notched by the foramen. The pedicle issues through an 
opening composed partly of a large open triangular delthyrium in the ventral valve, 
and partly of a large semicircular notch in the cardinal edge of the dorsal valve replacing 
the dorsal umbo. The surface of the ventral valve is ornamented with fine raised 
radial lines. The punctation of the shell is fine, and the pore density in the ventral 
valve 160. The dimensions of the shell are :—Length 5 mm., breadth 5 mm., thickness 
1-25 mm. 
The hinge teeth are situated at the anterior edges of the delthyrium and are 
small, and not supported by dental plates. There are a few spicules in the sinuses of 
the ventral valve. 
The cardinal border of the dorsal valve is notched by a semicircular foramen 
between one-third and one quarter the total width of the valve. At the posterior corners 
of the foramen two short socket ridges project slightly beyond the cardinal border, 
leaving two small semicircular hinge sockets at their outer sides. There is no sign of 
crura or primary loop lamellae. A simple thin septum, highest at its posterior end 
arises from the median line a little in front of the middle of the valve. The lophophore 
is reniform in shape, occupying five-eighths the length of the valve and seven-tenths 
of its width and has a slight forward indentation near the foramen, and a deep posterior 
invagination in front where it passes behind the septum. It contains a single row of 
cirri, which were strongly coiled towards the interior in the dead shell, and give a serrate 
appearance to the outer border of the lophophore. The cirri are apparently divided by 
numerous transverse partitions. The lophophore is supported by a row of spicules 
rising obliquely outwards from the floor of the valve and from the top of the septum. 
These spicules continue all the way around the lophophore and are most crowded behind 
the mouth, but in front of it there is a space free from them, bounded on each side by 
two large spicules which pass back from the posterior base of the septum like two large 
prongs. 
Further material is necessary for a better knowledge of the viscera and the 
muscles. The single specimen had been dead and rotting for a fortnight before it came 
into my hands. 
