BRACH10P0DA—THOMSON. 
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Genus Stethothyris Thomson, 1918. 
Stethothyris uttleyi sp. nov. 
(Plate XV, figs. 27, 28.) 
In order to base a new genus on this species, it is necessary to give here a brief 
diagnosis. The internal parts have already been described. The shell is of moderate 
size, elliptical, with gently rounded sides and a truncate front. The hinge line is of 
moderate breadth and obtusely angled. The lateral commissures are nearly straight, 
but the anterior commissure shows a flat-bottomed ventral depression of moderate 
width, corresponding to which there is a shallow anterior median sinus in the dorsal 
valve and an obscure median fold in the ventral valve, flattened anteriorly. The valves 
are moderately and nearly equally convex, the greatest thickness of the ventral valve 
being about the middle, and of the dorsal a little anterior to the middle of that valve. 
The beak is of moderate length, sub-erect, with fairly prominent beak ridges and a rather 
small mesothyrid foramen. The deltidial plates are fairly high and are transversely 
striated, often with a prominent median cord. The species differs from S. pedoralis 
(Tate) in its much shorter median dorsal sinus, its less incurved beak and correspondingly 
less convex pseudodeltidium, and its broader hinge line. 
Type locality .— Tuff band, Weston’s Quarry, Weston, near Oamaru, New Zealand. 
Horizon Ototaran, probably Lower Miocene. The species was discovered by Mr. G; 
Uttley, after whom it is named. 
The holotype is not the specimen here figured, and is in the Dominion Museum, 
Wellington. 
Stethothyris Antarctica sp. nov. 
(Plate XV, figs. 24, 25, 26; plate XVX, fig. 39.) 
Habitat. —Station 10; off Shackleton Glacier (Davis Sea), 325 fathoms, 29th 
January, 1914. Sea-bottom,-qqze ; temperature 1-65° C. 
The material consists of the united posterior end of both valves, and a separate 
fragment apparently of the anterior and left side of the ventral valve of the same 
specimen. The shell was evidently larger in size than any known Antarctic species, 
and must have been 50 mm. or more in length. The ventral valve is strongly convex, 
and the dorsal much less so. The beak has only moderately pronounced beak ridges 
and a fairly large mesothyrid foramen. The dorsal view of the united parts strongly 
recalls that of Magellania venosa as figured by Fischer and Oehlert (1891, plate XI, 
figs. 12, 13), but the characters of the cardinalia of the dorsal valve prevent an association 
with that species or with Waldkeimia kerguelensis Davidson. The septum bifurcates 
narrowly before joining the cardinalia, and the two branches, instead of uniting with 
the crural bases, as in Neothyris , run backwards towards the cardinal process, which 
is small and transverse as in Magellania. The socket ridges are very massive and broad 
posteriorly. The branches of the bifurcating septum overhang somewhat on each side. 
