CLASS BRACHIOPODA 
223 
the centre, hinge plates supporting two slender, curved lamellae; dental 
plates diverging. The foramen is at first only an angular notch in the 
hinge line of the ventral valve, but the growth of the deltidium usually 
renders it complete in the adult shell. (Tryon S. S. Conch.) 
Type. Anomia psittacea Gmelin. 
Distribution. Labrador, Hudson’s Bay, Melville Island, Sitka, Icy 
Sea, New Zealand. 
Range in time. Lower Silurian; North and South America, Europe, 
Thibet, China. 
Hemithyris psittacea Gmelin, 1792. 
Plate 16, figs. 8, 9, 10, 11, 12. 
Gmelin, Syst . Nat ., 2:3348. 
Shell somewhat triangular, globose, broadest anteriorly, tapering pos¬ 
teriorly; lateral margins rounded. Dorsal valve inflated, especially at the 
umbo, more or less divided into three lobes, of which the central one 
forms a mesial fold, scarcely defined in some specimens, much more so 
in others; front line nearly straight or three-lobed. Ventral valve much 
less convex than the dorsal one, rather flattened, with a broad, channelled, 
flattened, longitudinal, mesial sinus; beak sharply pointed, incurved, under 
which is situated an incomplete elongated foramen, margined anteriorly by 
the umbo, and laterally by triangular, deltidial plates; beak ridges not 
sharply defined; lateral margins of the valves sinuous, curved in front. 
Surface of valves radiately and finely striated. Shell structure fibrous. 
Valves strongly articulated by curved teeth in the ventral valve, fitting 
into sockets in the dorsal one. Hinge plate in the dorsal valve deeply 
divided, supporting two short, flattened, grooved and curved lamellae. At 
the bottom of the dorsal valve are seen the quadruple muscular impressions 
left by the adductor or occlusor muscles, each pair being separated by a 
short medio-longitudinal ridge. In the interior of the ventral valve the 
teeth are supported by dental plates extending to the bottom of the valve, 
and at their base a semi-circular ridge on either side encloses a saucer¬ 
shaped depression in which are situated the muscular scars. Close under 
the beak the peduncular muscles leave a small scar; lower down and 
toward the centre of the valve is situated a divided, heart-shaped scar, due 
to the adductor or occlusor muscles; and on each side of these are 
situated, one above the other, the divaricator and ventral adjuster muscular 
impressions. Colour bluish or a brown black. Length, 1 inch, 3 lines;. 
width, 1 inch, 1 line; depth, 9 lines. (Davidson.) 
Type in British Museum? Type locality, Mari Groenlandise. 
Range. Arctic Sea, Greenland, Spitzbergen, Norway, Shetlands, 
Hebrides, Orkneys, Northumberland coast, Labrador, Gulf of St. Law- 
