650 TRANS. OF THE ACAD. OF SCIENCE. 
face marked with broad concentric, imbricating lamella, 
which are often recurved from the surface of the shell; shell 
punctate. 
Length, .80; breadth, .95; thickness, .45. 
is shell is found in the Chemung rocks at Hannibal and 
Louisiana, and at Sulphur Springs, St. Louis county. 
convex, highest near the beak; mesial sinus obsolete or en- 
This fossil is most like Sp. hirsuta of Prof. Hall; but it 
may be distinguished by its greater thickness near the beaks, 
ca by the sharp thin edge found at the junction of the 
valves 
Abundant in some beds of the Hamilton rocks of Calla- 
way county. 
SerntGera MissourieEnsis, n. sp. 
Shell small, depressed, sub-orbicular or transversely ellipti- 
cal; ornamented wi valve 
slightly raised and rounded in front; beak ineurved tn 
and partly closing the perforation of the opposite beak in 
adult specimens. Surface ornamented with numerous con- 
centric, imbricating, transversely costate lamell - 
falling off leave granulated ridges. It is also senda wh 
small longitudinal strie; structure punctate. re 
Large specimen—Length, .50; breadth, .62; thickness, é 
This beautiful shell very much resembles Sp. sere 0 
gtd but that is ornamented with spines instead 0 
elle 
Rare in the Coal Measures of Montgomery and Chariton 
counties, 
