902 Report oF THE State GEoLoaIst. 
External surface covered with flexuous lines of growth. 
Shell-substance punctate in the inner layers. 
Type, Lyttonia nobilis, Waagen. 
Distribution. Carboniferous. 
Oldhamina, Waagen. 1883. 
Shells highly concavo-convex. 
Pedicle-valve subhemispherical; apex incurved, at maturity 
covered by a callosity, as in BrtirropHon; attached by cementa- 
tion in early growth. Hinge-line short and straight, not inter- 
rupted in the middle; below it lie well-developed teeth. Interior 
surface of the valve covered with diverging lateral ridges. 
Brachial valve concave. Cardinal process inconspicuous, quad- 
ripartite at the summit; continuous with a median ridge extend- 
Fia. 657. Fie 658, 
Oldhamina decipiens, de Koninck. 
Fia. 657, The interior of a pedicle-valve; showing the median and Jateral ridges. 
Fig. 658. The exterior of a pedicle-valve with the shell partly exfoliated. (WaAaGEN.) 
ing the entire length of the valve. Internal surface covered with 
divergent grooves corresponding to the ridges of the opposite 
valve. 
Exterior smooth or with numerous concentric lines of growth. 
Type, Oldhumina decipiens, de Koninck (sp.). 
Distribution. Carboniferous. 
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