224 Monograph of the LamelUbranchiafa. 



concave, and nearly vertical above, but rounding regularly into the 

 base below; beaks terminal, rather pointed, rising little ,bove the 

 hinge line, and directed a little obliquely upward and fc /ard, with 

 more or less inward curvature. 



Surface marked by 24 to 28 simple, strong, radiating costa3 to each 

 valve, that are nearly equal in breadth to the furrows between ; those 

 on the central portions of the valves passing nearly straight from the 

 lieaks obliquely to the posterior basal margins, those on the anterior 

 side curving more or less forward below, and those near the cardinal 

 margin curving a little upward behind. Crossing all of these cost® 

 and the furrows between, are numerous fine crowded lines, and at 

 regular distant intervals, a few strongly defined imbricating marks of 

 growth that curve parallel to the basal and posterior margins. 



Height, 2.30 inches; breadth, 2.20 inches; convexity, about 0.80 

 inch. Found near Freeport, Warren County, and in Clinton County, 

 Ohio. 



Anomalodonta Cosd — (Meek and Worthen). 



Shell trigonal, compressed, subequi valve, extremely inequilateral, 

 posterior side long, compressed and strongly alate ; the wing very large, 

 produced, pointed, and not separated from the alate posterior margin 

 by a distinctly defined sinus ; margin bebw the wing sloping ol> 

 liquely forward to the basal angle ; cardinal margin the longest part 

 of the shell, straight, and much compressed from immediately behind 

 the beaks ; anterior side truncated nearly vertically from the beaks, 

 about half way down the front, thence sloping slightly backward to 

 the basal angle ; basal margin produced downward, and terminating 

 in a distinct angle, slightly in advance of the middle. Umbonal slopes 

 very prominent, angular, or sometimes apparently bicarinate, straiglit, 

 and extending from the beaks, near the anterior margin, to the most 

 prominent part of the base, ranging at an angle of about sixty-five 

 degrees below the horizon of the hinge line, and provided with a longi- 

 tudinal sulcus below the middle of the valves. Beaks straight, rising 

 a little above the cardinal margin, and quite terminal. Surface orna- 

 mented with distinct, irregular, alternately larger and smaller thread- 

 like radiating strice, with less distinct concentric lines, and a few dis- 

 tinct, stronger marks of growth, which sometimes form prominent, 

 imbricating subspinous projections on the umbonal angle. 



Length, 2 inches; height, Vlo inches; convexity, 0-64 inch. 



Found in the upper part of the Cincinnati Group, at Richmond, 

 Indiana. 



