^ ^ . , LA.MELLIBEANCHIATA. 



liyrodesma major.] 



Ltrodesma major TJlrich. 



Cleidophorus major Uleich, 1879. Jour. Gin. Soc. Nat. Hist., vol. ii. p. 25. 



611 



Fig. 45. a, right valve of Lyrodesma major Ulrich; b, cardinal slope of same, x 2, showing the fine 

 radiating striae; 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; /, 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 i^rodesma acuminatum, y ax. intermedium, from the Trenton near Burgin, Ken- 

 tucky, i, dorsal view of a cast of the interior of Technophorus extenuatus Ulrich, x 2, showing the 

 united beaks, the flattefeing 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 28 mm., greatest hight of 

 same (from beaks to basal margin) respectively, 11, 15 and 18 mm.; greatest thick- 

 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 striae. 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 



