Fauna of the Morrow Group 
203 
anteriorly by lateral ridges and in the brachial valve of the two 
lateral sinuses defining the mesial fold serve to distinguish C. 
ovata from the larger individuals of C. ozarkana to which it 
appears to be closely related. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Stations 136, 139, and 149). Brentwood 
limestone: near Fayetteville, Arkansas (Station 135). Kessler 
limestone: near Brentwood (Station 144), and on East Moun- 
tain, Fayetteville (Station 209), Arkansas. Morrow formation: 
near Choteau, Oklahoma (Station 302). 
Composita deflecta n. sp. 
Plate XIV, figures l-3h. 
Description. Shell slightly under medium size, sub-pentagonal 
in outline, longer than wide, greatest width anterior to middle, 
valves sub-equally convex, anterior margin truncated by a sharp 
downward deflection of the mesial portion of pedicle valve. The 
dimensions of three nearly perfect individuals are: length, 20.2 
mm., 19.9 mm., 16.9 mm. ; width, 17.6 mm., 18.5 mm., 15.4 mm. ; 
thickness, 10.2 mm., 10.8 mm., 8.7 mm. 
Pedicle valve strongly convex in the umbonal region but with 
lessened curvature anteriorly and laterally ; mesial sinus consist- 
ing of a sulcus, ordinarily faint and ill-defined, originating in 
the umbonal region at some distance from the beak and con- 
tinuing to the anterior margin with little increase in depth or 
width; the middle three-fifths of the anterior portion of the 
valve notably extended and deflected sharply downward forming 
an angle of 50° to 80° with the plane of union of the two valves 
and truncating the anterior margin; deflected area outlined by 
two lateral ridges, not elevated above the valve surface but 
formed by the downward flexure in front and the normal lateral 
curvature behind, converging rapidly posteriorly but not defined 
in the mesial portion of the valve, anterio-lateral margins border- 
ing the deflected extension flattened or crimped upward along 
line of contact between valves; beak somewhat elevated, not 
tumid, incurving above that of brachial valve less markedly 
than is common among Compositas, truncated by the sub-circular 
foramen; delthyrium triangular, not always concealed by beak 
of brachial valve. 
