288 PALEONTOLOGY OF NEW YORK. 



end to the post-basal extremity, abruptly recurving and extending thence in 

 a nearly direct line to the cardinal margin ; cardinal margin nearly straight. 

 Anterior end short, rounded, without any indication of limitation by a sinus 

 or otherwise. 



Valves moderately convex, scarcely gibbous in the umbonal region. 



Hinge-line straight, extending about half the length of the shell. 



Beaks sub-anterior, small, closely appressed, rising but little above the 

 hinge-line. Umbonal region defined, sub-angular; the slope straight and 

 rigid, extending from the beaks to the post-basal extremity. 



Test thin, marked by fine concentric stria), which are rarely fasciculate 

 and elevated into ridges. Interior unknown. 



A medium-sized specimen has a length of 41 mm., and a height of 22 mm. 

 A smaller specimen measures 30 mm. in length and 17 mm. in height. 



This species bears some resemblance to M. subalata, but is less alate on the 

 posterior slope ; the umbonal ridge is more direct, the post-basal extremity is 

 directed more downward, basal margin more regularly convex and without 

 evidence of a sinus. 



The original reference of figs. 10 and 11 of plate xli to this species is 

 erroneous, those figures representing the Chemung variety of M. subalata. 



Formation and localities. In the sandstones of the Chemung group, near 

 Angelica; and at Rock creek, Alleghany county, N. Y. 



MODIOMORPHA RECURVA. 

 PLATE XLI, FIG. 17. 

 Hodiumorpha recurva. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 41, fig-. 17. 1883. 



Shell of medium size, ovate-sub-cuneate ; length about twice the height ; basal 

 margin regularly curving to the anterior and posterior extremities. Posterior 

 end acute, recurving very abruptly toward the cardinal line. Cardinal margin 

 arcuate or nearly straight. Anterior end short, abruptly rounded, limited 

 posteriorly by a very shallow and undefined sinus (which is much too strongly 

 represented in the figure). 



