28 AUSTRALASIAN ANTARCTIC EXPEDITION. 
as if in process of evolution to hinge plates of the Magellaniform type, but the process 
is not far advanced. The shell substance is thick, and the pores rather large and circular, 
with a density of only 60 to 70 on the fragment of the anterior border. 
The type of cardinalia above described agrees so nearly with that of Stethothyvis 
pectoralis Tate (plate II, fig. 2) that there can be little doubt the two species are congeneric. 
Although the material is fragmentary the characters of the cardinalia render the 
identification of more perfect examples easy, and for the purposes of convenient reference 
I venture to give the species a name. 
Genus Gyrothyris Thomson, 1918. 
Gyrothyris mawsoni sp. nov. 
(Plate XV, Figs. 1, 2, 3, 4, 5.) 
Habitat. —One mile off south end of Macquarie Island. 
Shell ovato-triangular, with a narrow beak and rounded sides and front, the 
latter slightly produced. The hinge line is narrow and strongly curved. The dorsal 
valve is only moderately convex, with steep slopes near the umbo, and an indistinct 
frontal sinuation. The ventral valve is strongly convex posteriorly, becoming flatter 
in front, and has an indistinct median fold. The commissure is straight on the sides 
and shows a broad, shallow ventral depression in front. The beak is of moderate length, 
narrow but swollen, erect, and without pronounced beak ridges. It is truncated by 
a foramen of moderate size, apparently mesothyrid in position and attrite in condition. 
The pseudodeltidium is almost hidden, and is low, narrow, and concave. The surface 
of the single specimen is much obscured by encrusting bryozoans, but shows fairly 
strong growth lines, and an obsolete radial costation a little more prominent than that 
present in Terebratella rubicunda and of similar fineness. This radial ornament is not 
brought out in the illustration owing to lighting of the specimen from both sides. Owing 
to the encrusting organisms, the pores could not be counted. 
The characters of the interior and the relationships of the species have been 
described above. 
Genus Magellania Bayle, 1880. 
Genotype Terebratula flavescens Val. 
Magellania joubini Blochmann. 
( Plate XV, figs. 6, 7; plate XVI, figs. 33, 34, 41.) 
1906. Magellania joubini Blochmann, Zook Anz., Bd. XXX, p. 697. 
1907. Magellania sulcata Smith, National Antarctic Expedition, 1901-1904. 
Natural History, Zoology, vol. 11, Brachiopoda, pp. 1, 2, figs. 3, 4. 
1908. Magellania joubini Blochmann, Zeitschr. f. wissensch. Zook, Bd. XC > 
p. 609. 
