ORDER I 



AT1IK.MATA 



307 



Tin- family contains the oldest LiliguloiJ shells, the member.* of which still retain 

 a preponderance of Oboloid characters. The first true Linyulae appear in the Lower 

 Ordovician. 



, 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-likr muscular 

 scars, while those of the type species seem to be more in harmony with /,/////>///. 



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 

 bifurcated terminally. Ordovician ; North America. 



(?) Pater-Ida, Barrande. Ordovician ; Bohemia and North America. 

 (?) 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 ^<"Y>. 

 two of adductors, and four of sliders, or ailjnstors. 

 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 

 FIG. 509. FIG. 510. preceding, but interior of ven- 



Lingulaanatina, Brug. Recent. A, Shell I Ltn - <>w. tral valve with two SCDtal 



with pedicle. ^Interior of ventral valve. Silurian ; Gottland. ^^ 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. 



