LAMELLIBRANCHIATA. 471 



truncate. Cardinal line straight. Anterior end short, obliquely truncate 

 above, and narrowly rounded below. 



Valves of moderate convexity below and posteriorly, gibbous in the umbo- 

 nal region. 



Beaks sub-anterior, prominent, arcuate and projecting above the hinge- 

 line. Cincture obscure, scarcely perceptible, except toward the base of the 

 shell, where it produces a slight sinuosity in the striae and basal margin. 

 Umbonal .slope distinctly angular, extending to the post-inferior extremity. 

 Post-cardinal slope wide, distinctly limited. 



Surface marked by fine concentric .stria;, which become fasciculate, and 

 by strong undulations on the anterior and middle portions of the shell. 

 Radiating striae sometimes mark the body of the shell, but are often obscure 

 or obsolete. 



Three specimens measure respectively 10, 16 and 18 mm. in length, and 

 6, 9 and 9.5 mm. in height. 



This .species bears much resemblance to P. radiata, but the prevailing forms 

 are smaller, the concentric undulations are much stronger and the radii are 

 obscure or obsolete. This form, however, may prove to be only the immature 

 condition of P. radiata. 



Formation and localities. In the shales of the Hamilton group, at Fabius, and 

 on the shore of Skaneateles lake, N. Y. 



Pholadella Newberryi. 



PLATE LXXVUT, FIG. K. 



PholarMla Nrwl>err!ji. Hku.. Prelim. Notice Lamellibi-anchiatfi, 2, p. fi.'i. 1870. 



Pal. N. Y., vol. V, i>t. 1. Plates anil Kxpl.inations: PI. 78, fig. 2.5. 1883. 

 AllorUnna (fted-gicirkin f) pleiinqrixtha^ Mekk. Proc. Acail. N.-it. Soi., Phila, \ol. 23, p. 14. 1871. 

 " (CercnmynpsiJi) " " Pal. Ohio, vol. 11, p. 309, pi. 13, fiffs. 4a, b, c. 1873. 



Shell large, elongate-ovate, sub-falcate; length less than twice the height. 

 Ba.sal margin regularly curving, with a gentle sinuosity anterior to the 

 middle. Posterior extremity vertically or somewhat obliquely truncate. 



