356 
PALAEONTOLOGY OF NEW YORK. 
posterior slope reaching to the posterior margin. This feature is also 
obscurely shown on several of the older individuals (erroneously represented 
in fig. 21). 
Cardinal teeth not determined. One or two lateral teeth are present on 
the cardinal alation, extending nearly to the posterior extremity. Anterior 
muscular impression strong. 
Five characteristic specimens measure respectively 23, 36, 38, 39 and 41 
mm. in length, and 16, 24, 25, 27 and 28 mm. in height. 
This species is readily distinguished from the known species of the genus by 
its short, broad form and alate post-cardinal extension. 
Formation and localities. In the shales of the Hamilton group, at Fultonham 
and Summit, Schoharie county, N. Y. 
Nyassa recta. 
PLATE LIII, FIGS. 1-6. 
Nyassa recta, Hall. Prelim. Notice Lamellibranchiata, 2, p. 29. 1870". 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 53, figs. 1-8. 1883. 
Shell small or of medium size, ovate sub-cuneate; length nearly twice the 
height; basal and cardinal margins sub-parallel; basal margin gently curv¬ 
ing or often nearly straight, abruptly recurved at the post-inferior angle and 
more gently curving at the anterior end. Posterior extremity obliquely 
truncate. Cardinal line straight or slightly arching, and declining toward 
the posterior end. Anterior end short, narrowed and regularly rounded 
below the beaks. 
Valves regularly convex in the lower part, gibbous above and in the 
umbonal region. 
Beaks sub-anterior, prominent, rising above the hinge-line. Umbonal 
ridge direct to the post-inferior extremity, with usually a slight flattening or 
depression in the shell below the ridge, which extends from the umbo to the 
base, scarcely constricting the margin. 
