136 PALEONTOLOGY OF NEW- YORK. 



Linirala perlata ( n. s.)- 



Plate IX. Fia. 3-5. 



Shell ovate : beaks subacute : base broadly rounded, having the greatest 

 width a little below the centre. Valves equally convex. 



Surface marked by close concentric lines of growth, the impression of 

 which is preserved when the outer shell is removed. Exfoliated surface 

 marked by faint concentric ridges, corresponding to those on the 

 exterior, and fine scarcely visible longitudinal strife. 



In the specimen fig. 4, the striae are generally very closely arranged ; though 

 certain portions of the surface present these markings comparatively distant, de- 

 pendent doubtless on the rate of growth in the shell. 



In the specimen fig. 5, the strise on the upper part of the shell are distant three 

 or four times their width, while those on the lower part are close together. These 

 variations, and the want of perfect agreement in the surface characters, are scarcely 

 of specific value; and without a larger number of specimens, it would be unwise 

 to make distinctions. 



Fig. 4. An individual of medium size, preserving the two valves. The outer shell is partially 



exfoliated from the central part of the valve. 

 Fig. 3. Profile of the same specimen, showing the convexity of the valves. 

 Fig. 5. The lower part of a larger valve having the striao more distant, very thin and 



sharply elevated, while towards the margin they are more closely arranged. 

 Fig. 5 a. Enlargement of the concentric lamellae. 



Geological position and locality. In the Pentamerus limestone (specimen no. 5), 

 and in the shaly limestone of the Lower Helderberg group : Albany and Schoharie 

 counties. 



Lin«;u1a rectilatera ( n. s.). 



Plate IX. Fig. 6 & 8. 



Shell subelliptical : sides parallel, abruptly curving towards the base 

 and beak : base abruptly rounded or sub truncate. Cardinal margins 

 nearly straight, very convex in the middle and subobtusely carinate 

 towards the beak, which sometimes extends a little beyond the body 

 of the shell in an acute point. 



