460 PALEONTOLOGY OF NEW YORK. 



P ROTH Y III S, Meek. 1869. 

 Prothyris planulata. 



PLATE LXXVl, FlU. 1 ; and PLATE XCIV, FIG. 8. 

 Prothyris plawdata. Hall. Pal. N. Y., vol. v, l>t. 1. Plates and Explanations: PI. 7ti, fig. 1. 1883. 



Shell small, Ugulate ; 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. 



Valves 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 stria3, which are aggregated into ftis- 

 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 LXJCVI, FIGS. i-8. 

 Prothyrit lanceolata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 7(), 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 



