SHUMARD AND SWALLOW—NEW FOSSILS. 219 
Ortnistina Missovriensis, Swallow. 
ve te; mate rena rrow, potete: or saartona Bop 
vat cram, "extending from the base of the area to the 
entral v 
beak, aig htly flattened towards the anterior m margin; area ob- 
solete; beak small, in contact with the deltidium. Each valve 
is marked with obscure, concentric ruge or lines of growth, 
and from ten to fourteen large, strongly carinated, radiating 
ribs, which become eee be and smaller in the middle and 
near the beaks; the surface is also ornamented with 
diagonally back to the bottom of 
he channel ; ¢ transverse strie are smaller, more obvious 
between the longitudinal lines, concentric towards the beaks ; 
but on the a they cross the other ‘set of strip nearly at 
angles. The longitudinal strie are themselyes some- 
irkec with very fine nodular line o by rows: Ay Bt . 
eo ghana: to pentagons, gibbous 
eR 0 the ront sei or angular; sides enrene 
oo beak, where m ‘pr an arfgle © ng 
0111 US petra 4 oie | near the be 
