46 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Not Pandora trilineata Say, 1822, Jour. Acad. Nat. Sci. Philadelphia, 1st 



ser., vol. ii, p. 261. 

 Pandora (Clidiophora) trilineata Say, 1903, Dall, Trans. Wagner Free Inst. 



Sci. Philadelphia., vol. iii, pt. vi, p. 1519 (ex parte). 



General Characters. — Shell rather small, rather thin. Trans- 

 versely alate in outline, slightly flexuous, compressed. Inequi- 

 valve, but only to slight degree. Strongly inequilateral. Um- 

 bones very low, the apices usually perforate, strongly anterior 

 but not terminal. Lunule absent. Escutcheon sub-linear, almost 

 as long as the posterior dorsal margin, strongly angulated upon 

 its outer border. Anterior end of valve sharply rounded or ob- 

 tusely pointed. Posterior dorsal margin gently convex. Sub- 

 marginal carinas very sharp, wider and more depressed posteriorly 

 in the left valve than in the right. Ventral margin curving wing- 

 like from the anterior expansion to the posterior rostrum. Margin 

 in front of the rostrum contracted in the left valve by the ante- 

 rostral depression. Right carina outlined by a linear sulcus. 

 Anterior area between one-third and one-half the entire valve, 

 differentiated only in the left valve, and then merely by a more 

 or less obsolete, linear sulcus and the abrupt upcurving of the 

 growth lines toward the front. 



Sculpture. — Radial sculpture usually absent even in the right 

 valve. Incremental sculpture fine, irregular, often discontinuous, 

 with no very pronounced resting stages. 



Ligament. — Ligament entirely enternal; lodged in the right 

 valve, between the middle and posterior cardinals and, in the 

 left valve, in a bilobed pit, posteriorly produced beneath the dorsal 

 margin. 



Dentition. — Hinge dentition moderately robust. Anterior car- 

 dinal of right valve obsolete. Middle cardinal compressed, rhom- 

 boidal or hatchet-shaped. Posterior cardinal compressed, ob- 

 liquely produced, often acutely pointed medially or ventrally. 

 Anterior cardinal of left valve a moderately prominent ridge of 

 uniform elevation extending from the umbones to a point just 

 dorsal to the medial line of the anterior adductor. Posterior 

 cardinal linear, inconspicuous, seated upon the anterior edge of 

 the resilial pit. 



Muscle Impressions and Pallial Line. — Adductor muscle impres- 

 sions slightly sunken, irregularly rotund. Pallial line punctate, 

 non-sinuous, nearer the base anteriorly than posteriorly. 



Dim£7isions.- — Altitude, 9.5 mm. Latitude, 2L0 mm. Semi- 

 diameter (left valve), 2.0 mm. 



