The Genera of Brachiopoda. 
CHARACTERS AND DISTRIBUTION OF THE 
GENERA OF BRACHIOPODA. 
BY CHARLES W. ROLFE. 
{Based mainly on external characteristics^ 
I. Valves not united by a hinge, but kept in position by muscular 
action {a), 
{a) Shell structure horny {b). 
{b) Valves nearly equal, shell hatchet-shaped, or quadrate 
{bb). 
{bb) Beaks equal, projecting, pointed, 
without a groove between them for 
the passage of the foot, Lingula Brg. 
Subgenera : 
Forms with the beaks unequal, Liiigtilcpis Hall. 
Forms with groove, Lingulella Salter. 
{b) Valves unequal, shell rounded or oval, dorsal valve the 
larger {c). 
(c) Dorsal valve limpet-shaped, smooth 
or concentrically striated, ventral valve 
slightly convex, with a rounded or 
oval opening behind the beak, which 
does not reach the margin, Discina Lmck. 
Subgenera : 
Forms in which the opening for the 
foot lies at the posterior end of 
the furrow, Orbiculoidea d'Orb, 
Forms in which the ventral valve 
is flat or concave, and the fora- 
men is narrow and slit-like, Discinisca Dall. 
{b) Valves unequal, ventral valve the larger {cc). 
(cc) Surface smooth, form somewhat 
triangular, ventral valve high-con- 
ical, with a flattened area running 
