232 NEW YORK STATE MUSEUM 



the surface is slightly concave in this region. On the anterior margin the 

 slope is abrupt and vertical for a short distance to the hiatus, but the sicae 

 are comparatively narrow. 



Surface markings consisting of radial plications crossed by fine concen- 

 tric lines ; of the same character as in L. acutirostrum. The number 

 of these plications is usually 47, but may vary from 45 to 55. Those on the 

 posterior slope are the coarsest and are separated by the widest furrows. 

 Directly behind the beak and at the side of the triangular cardinal area 

 the first two or three of the plications are stronger than the rest, their free 

 edges making processes which interlock on opposite valves. 



Dimensions. A full grown example of normal form is 54 mm in hight, 

 47 mm in length ; the sical margin measuring 36 mm in length. A smaller 

 specimen which has been subjected to no distortion is 32 mm in hight ; 35 

 mm in length, and the sical margin 23 mm in length. 



Habitat. Genesee province ; Naples subprovince. This species is 

 widely distributed and is of more frequent occurrence than its ally, P. 

 acutirostrum. It is found in the lower shaly beds and rarely in the 

 higher sandstones of Ontario, Livingston, Genesee, and Wyoming counties. 

 Occasionally in the upper part of the Havana glen section, Schuyler co. ; 

 and at Himrods and Branchport, Yates co. It has not been observed in 

 the lower shales of Erie county. 



Lunulicardium (Pinnopsis) libum sp. nov. 



Plate 2, fig. 40; plate 4, fig. 1, 2 



This form is characterized by subacuminate valves, broadly rounded 

 and subsemicircular on the pallia! margin. Beak nearly in the axial line. 

 Sical margin oblique, rather longer than one half the hight of the shell, 

 incurved and slightly arched. Sicae very broad and smooth, usually ver- 

 tical but extended obliquely or horizontally by compression. Surface of the 

 shell with from 15 to 25 low, broad, flat topped plications with narrower 

 intervals. These plications are all simple in the umbonal region, but bifur- 

 cate rapidly and irregularly over the pallial region, so that in full growth 

 they present the appearance of great inequality specially if the multiplica- 



