LAMELLIBRANCHIATA. 611 
Lyrodesma major.) 
LyropEsMA MAJOR Ulrich. 
Cleidophorus major ULRICH, 1879. Jour. Cin. Soc. Nat. Hist., vol. ii, p. 25. 
Fig. 45. a, right valve of Lyrodesma major Ulrich; 6, cardinal slope of same, x 2, showing the fine 
radiating strive; c, interior of a right valve; d, hinge of same, x 2; e, left side of a cast of the interior of 
same, Showing the muscular scars and pallial line with unusual distinctness; f, dorsal view of same, slightly 
enlarged; g, vertical section through a valve at the beak, showing thickness of hinge plate and why the 
beaks in casts are widely separated; specimens from upper beds of the Cincinnati group at Clarksville, 
Ohio. h, right valve of Lyrodesma acuminatum, var. intermedium, from the Trenton near Burgin, Ken- 
tucky. 7, dorsal view of a cast of the interior of Technophorus extenwatus Ulrich, « 2, showing the 
united beaks, the flattening of the posterior dorsal edge and other features. 
Shell transversely subovate, unusually elongate for the genus, narrow poste- 
riorly; length of three testiferous examples 17, 24 and 25 mm., greatest hight of 
same (from beaks to basal margin) respectively, 11, 15 and 18 mm.; greatest thiek- 
ness subcentral, somewhat greater than half the hight; anterior margin rounded, 
most prominent immediately above the middle of the hight, often straightened in 
the upper half to the beaks; base broadly yet rather strongly convex; posterior end 
long, somewhat attenuate, narrowly rounded at the extremity; cardinal outline 
declining each way from the beaks, more or less concave behind them. Beaks rather 
prominent, small, incurved, situated about one-fourth of the entire length from the 
anterior extremity; umbones full, sharply rounded on the posterior side where the 
surface descends abruptly to the cardinal margin; behind the beaks the dorsum is 
first concave, then flat and finally low ridge-shaped; beneath, or rather in front of 
them, there is an impressed line on each side which defines an elongated lanceolate 
area. Surface nearly smooth, in one example exhibiting fine concentric stria. All 
of the testiferous specimens however have twelve or more, fine radiating lines on 
the posterior umbonal ridge and cardinal slope. 
Hinge with six teeth in each valve, the four central ones much stronger than 
the marginal pair. Muscular scars strongly impressed, the anterior adductor sharply 
defined on the inner side by a thin ridge running down from the hinge, narrowing 
above and surmounted by deep supplementary scars; posterior adductor elevated 
