The American Naturalist. 
[Nc 
ribbed. Small valve with a 
sinus, large valve with a fold, Camerella Bill, 
(//) Shell usually more or less 
triangular, rarely globose or 
transversely oval. Beak sharp, 
directed forward, or sharply 
incurved. Larger valve with 
a sinus, smaller with a fold, Rhynchonella Fisch. 
{pp) Like Rhynchonella, but the 
inside of the ventral shell has 
converging tooth plates, which 
unite to form a low median 
septum, and the dorsal valve 
has a low, trough-like process, 
and high median septum, Camarophoria King. 
{p) Beak large and heavy {q). 
{q) Surface smooth, or concen- 
trically striated, rarely with in- 
dis 
ribs. Form 
varymg 
from ovoid to transverse, 
area. Interior with spires. 
Ventral valve with two curi- 
ously curved plates, called 
" shoe-lifter processes," 
{q) Differs from Merista only in 
the absence of the shoe-lifter 
processes, 
{q) Differs from Meristella in 
that the two processes which 
form the loop connecting the 
spires do not diverge again 
after uniting, 
{q) Form varying from elongate 
to gibbous or rotund. Surface 
ribbed, rarely smooth. Ven- 
tral valve 
uch the 
larger. Beak very large and 
