300 PALAEONTOLOGY OF NEW-YORK. 



Mei'istella haskiiisi. 



PLATE XLIX. 

 Merittella haikinti ; IIall, Thirlecnlli Report on the State Caliiuel, p. 84. 18G0. 



Shell broadly ovate, more or less gibbous ; length and breadth nearly 

 equal, the greatest width anterior to the middle; slightly sinuate in 

 front. In many well-formed specimens the length and width are about 

 equal; when the length is greater, it is due to the extension of 

 the beak of the ventral valve. 



Yemtral valve regularly convex, often gibbous above the middle, and 

 curving regularly to the sides and more gently to the front, which is 

 sometimes a little impressed at the margin by a broad shallow sinus : 

 beak elevated, slightly incurved and broadly truncated by a circular 

 foramen. The triangular space beneath the apex is occupied by delti- 

 dial plates, which appear to be closely anchylosed in the centre. 



Dorsal valve usually a little wider than long, moderately convex in 

 young shells, gibbous in the middle and above in older specimens, 

 curving regularly to the sides and front, and scarcely affected by the 

 slight elevation near the anterior margin : beak short, and neatly 

 incurved beneath the deltidial plates of the opposite valve. 



Surface marked by fine concentric striae, which are raised and thread- 

 like, and sometimes crowded together in fascicles •. these appear also 

 to be indistinctly radiate or crenulate. In exfoliated specimens there 

 are sometimes distinct radiating striae upon the surface. 

 The rostral cavity of the ventral valve is narrow, the teeth are of 



moderate strength, and the dental plates reach the bottom of the cavity 



and extend forward ; the muscular area is broadly triangular and strongly 



striate. In the dorsal valve the muscular area is ovate or cordiform, and 



extends below the middle of the valve ; the low slender septum extends 



a little beyond the muscular area. 



This species is quite distinct, in its various phases, from the 31. barrisi, which 



. is more gibbous, with the ventral beak more closely incurved. In well-preserved 



