ORDER I ATREMATA 307 
This family contains the oldest Linguloid shells, the members of which still retain 
a preponderance of Oboloid characters. The first true Lingulae appear in the Lower 
Ordovician. 
Lingulella, Salter. Linguloid shells with the ventral cardinal area more 
or less elevated beyond the dorsal shell, and bisected medially by a narrow 
pedicle furrow, Cambrian; North America and Europe. 
This genus is not well known, and the species referred to it may belong to two 
_or more genera. The Lower Cambrian forms have decided Obolella-like muscular 
sears, while those of the type species seem to be more in harmony with Lingua. 
Lingulepis, Hall. Pedicle valve generally much produced at the beak, 
with no distinct cardinal area ; dorsal valve more or less ovate. Cambrian ; 
North America. 
Leptobolus, Hall. Very small Linguloid shells, with well-developed, dis- 
tinctly grooved, cardinal areas in both valves. Interior marked by two or 
three diverging, slightly elevated septa, which sometimes are somewhat 
bifureated terminally. Ordovician ; North America. 
(2) Paterula, Barrande. Ordovician; Bohemia and North America. 
(2) Mickwitzia, Schmidt. Lower Cambrian ; Sweden. 
Family 2. Lingulidae. Gray. 
Attenuate, sub-quadrate, or spatulate, almost equivalved Lingulacea, with a more 
or less long, tubular, flexible pedicle. Muscles 
highly differentiated and consisting of six pairs, 
two of adductors, and four of sliders, or adjustors. 
Ordovician to Recent. Maximum develop- 
ment in Ordovician, declining after Devonian 
time. 
Lingula, Bruguiere (s. g. Glossina, Phill.), 
(Figs. 509 and 510). Shell thin, usually com- 
pressed, glistening, generally smooth, or with 
fine, concentric, more rarely with both con- 
centric and radial striae; broad over the 
pallial region, tapering more 
or less toward the beaks. 
Ordovician to Recent. Maxi- 
mum development in Silurian 
and Devonian. 
Glottidia, Dall. Like the 
Fic. 509. Fia. 510. preceding, but interior of ven- 
Lingula anatina, Brug. Recent. A, Shell Lingula Lewisii,Sow. tral valve with two septal 
with pedicle. B, Interior of ventral valve. Silurian ; Gottland. ridges diverging . from the 
beaks. Dorsal valve with a single median ridge. Recent ; American seas. 
Dignomia, Hall. Both valves with median septal ridges; that of the 
dorsal valve stronger, and flanked by two submarginal diverging ridges, 
which correspond in position to grooves in the ventral valve. Middle De- 
vonian ; North America. 
Barroisella, Hall and Clarke. Lingulae with rudimentary articulation. 
Silurian to Devonian ; North America; (?) Bohemia. 

