460 
PALAEONTOLOGY OF NEW YORK. 
P 110 THY RIS, Meek. 1869. 
Protiiyms planulata. 
PLATE LXXVI, FIG. I ; AND PLATE XCIV, FIG. 8. 
Prothyris planulata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 76, tig. 1. 1883. 
Shell small, ligulate ; length more than twice the height. Basal margin nearly 
straight, curving anteriorly and truncate behind. Posterior extremity verti¬ 
cally truncate. Cardinal line long, straight, essentially parallel to the basal 
margin. Anterior end auriculate, limited from the body of the valve by a 
constriction and deep sinus in the margin. 
Yalves depressed-convex below, more convex above the middle of the shell. 
Beaks sub-anterior, low and inconspicuous. Umbonal slope angular, 
extending to the upper posterior extremity, below which is a shallow groove 
extending from the umbo to the post-inferior extremity. Post-cardinal 
slope narrow and concave. 
Surface marked by strong concentric striae, which are aggregated into fas¬ 
cicles along the basal margin. 
A specimen of ordinary size has a length of 17 mm. and a height of 7 mm. 
This species differs from P. elegans , Meek, in being proportionally higher, 
with convex basal margin, posterior extremity decidedly truncate, the umbonal 
slope distinctly angular with a shallow furrow below, extending from the beak 
to the post-inferior extremity, and in having more irregular concentric striae. 
Formation and localities. In the shales of the Hamilton group at the outlet 
of Crooked lake and near Norwich, Chenango county, N. Y. 
Prothyris lanceolata. 
PLATE LXXVI, FIGS. 2-8. 
Prothyris lanceolata, Hall. Pul. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 76, figs. 2-8. 1883. 
Shell of medium size, elongate-lanceolate; length three times the height. 
Basal margin very gently curving, often nearly straight on the anterior half. 
Posterior extremity pointed, very obliquely truncate above. Cardinal line 
about two-thirds the length of the shell. Anterior end truncate, margin 
