440 PALEONTOLOGY OF NEW YORK. 



PARACYCLAS, Hall. 1843. 



[ Type P. elliptica. ] 



Paracyclas elliptica. 



PLATE LXXII, FIGS. 2S-38 ; AJID PLATE XCV, FIG. 18. 



Paraeyclas elliptica. Hall. Geol. Surv. N. Y., Rep. Fourth Dist., p. 171, t 07, %. 2. 1843. 



Pal N. Y., vol. V, pt. 1 Plates and Kxplamitions : PI. 72, fig-s. 23-30. 1883. 

 Lueina {Panuyclax) elliptica, var. Occident aim. Hall and Wiiitkikld. Twenty-fourth Ann. Rep. N. Y. 



State MuB. Nat. Hist., p. 189. 1872. 



Shell large, sub-circular or broadly sub-elliptical (subject to great variation in 

 form from compression); length and height about equal. Pallial margin 

 regularly curving from the extremities of the hinge. Cardinal line short, 

 more than one-third the length of the shell, slightly arcuate. 



Valves regularly convex, somewhat regularly gibbous in the middle. 



Beaks a little anterior to the middle, small, appressed and closely incurved, 

 rising but little above the hinge-line. Umbonal slope defined above by a 

 depression extending from the beaks to about the middle of the posterior 

 extremity, distinctly limiting the post-cardinal slope of the valves. 



Test thin. Surface marked by fine concentric striae, which are aggregated 

 into fascicles at irregular distances. 



Ligamental groove narrow and elongate. Posterior muscular impression 

 just within the post-cardinal margin and below the ligamental groove. Pal- 

 lial line parallel with the basal margin, marked in the cast by a row of elon- 

 gate nodes, which are the terminations of low ridges from above. Interpal- 

 lial area pustulose on the cast. 



Five specimens measure respectively 30, 32, 40, 44 and 48 mm. in length, 

 and 29, 33, 37, 40 and 44 mm. in height. 



This species has been generally identified with Lucina proavia, Goldfuss 

 (Petref. Germ., pi. 146, fig. 6, p. 226), but the hinge of that species is much 

 more declining, and the anterior end is more elevated and sub-auriculate, as 

 shown in his figures, which are not features in the American form. 



