SWALLOW—DESCRIPTION OF FOSSILS. 651 
SPIRIGERA MAcONENSIS, n. 8p. 
Shell small, gibbous, varying from ovate to orbicular. Ven- 
tral valve rather convex, most elevated near the beak, whence 
it is regularly arched to the margins; beak large, incurved ; 
perforation orbicular or subovate ; mesial sinus well defined 
in front, but usually obsolete towards the beak. Dorsal valve 
somewhat smaller, sub-orbicular, most convex near the beak, 
slightly flattened towards the lateral margins ; convex along 
the middle, with a slight mesial sinus on the anterior portion 
of adult shells; beak curved beneath and usually breaking 
into the perforation of the opposite beak. Surface marked 
with numerous unequal, subimbricating, concentric plications. 
Large orbicular specimen—Length, .50; breadth, .50 ; thick- 
ness, .30. 
Large ovate specimen—Length, .55; breadth, .48; thick- 
ness, .35. 
Common in the Coal Measures of Montgomery county. 
SPrRIGERA CHARITONENSIS, Nl. Sp. 
Shell orbicular, lenticular; valves regularly and about 
equally convex; beaks small. Ventral valve very regularly 
convex; slightly most prominent near the beak; mes 
vex; slightly raised along the center into an obsolete mesial 
fold, which becomes more elevated and rounded in front.in 
adult specimens, which usually have a depressed line along 
the center of the mesial fold on the anterior half of the shell; 
small, incurved beneath the opposite beak. Surtace 
ie strie, Structure punctate. 
Length, 1.10; breadth, 1.10; thickness, .70. _ ») dk 
This fossil most resembles the Athyris (Spirigera : ) Aer: 
entius of Mr. McChesney, but it is more orbicular and re A 
arly ebealer, and the mesial sinus is much less developed, 
Specially towards the beak. 
Rare 8 the Coal Measures of Chariton and Randolph 
counties, 
SprriGERA JACKSON, 0. SP- 
Shell rather large, elongate, ovate, striate, punctate ; broad 
