The Genera of Brachiopoda. 
987 
a triangular opening, which 
is filled by the incurved 
beak of the smaller, Trcmatospira Hall. 
{k) Shell impunctate {m). 
(;«) Apex of spires directed towards ventral valve 
{mm). 
(mm) Shell ( 
{mm) Shell plano-convex, 
(m) Apex of spires directed to- 
wards dorsal valve. Shell 
piano- or biconvex. Surface 
with ribs and transverse lines 
of growth, 
(m) No spires («). 
(«) Shell piano- or slightly bi- 
convex. Ventral valve with 
a broad, deep sinus on its 
posterior margin, which 
reaches half-way to the beak. 
Dorsal with a marginal 
(«) Shell tranversely oval. Sur- 
face with cellular impres- 
sions arranged in rows, 
{kh) Beak not pierced by a foramen, (o). 
{o) Shell punctate (oo), 
{00) Shell spherical. Surface smooth 
or covered with hair-like spines. 
Beak light, sharp-pointed, with an 
area beneath, 
{00) Surface ribbed. Beak heavy. 
Ccclospira Hall. 
Zygospira Hall. 
Nuclcospira Hall. 
Amphigenia Hall. 
ip) Shell impunctate (/). 
(/•) Beak thin and sharp (//). 
{PP) Valves nearly equal. Shell 
smooth or faintly 
