402 
PALAEONTOLOGY OF NEW YORK. 
an obscure fold which may sometimes he obsolete. Cincture scarcely per¬ 
ceptible, sometimes producing a slight constriction in the inferior margin. 
Surface marked by fine concentric striae, which may be more or less fas¬ 
ciculate, producing gentle undulations of the surface. No radiating striae 
have been observed. 
Ligamental area narrow. Anterior muscular impression strongly marked. 
Five specimens measure respectively 29, 31, 46, 48 and 49 mm. in length, 
and 12, 13, 17, 17 and 18 mm. in height. 
The shell is proportionally longer and narrower than any of the preceding 
species, the form is more arcuate and there is no conspicuous fold on the jiost- 
cardinal slope. 
Formation and localities. In the Chemung group, at Philipsburgh, and in loose 
masses of sandstone near Portville and Olean, N. Y. 
Sphenotus rigidus. 
PLATE LXVI, FIO. 14. 
Ctjpricardia ? rigida, White and Whitfield. Proc. Bos. Soc. Nat. Hist., vol. viii, p. 300. 1862. 
In part iSanguinolites rigidus (White and Whitfield), Hall. Prelim. Notice Lamellibranchiata, 2, p. 44. 
1870. 
“ “ “ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Expla¬ 
nations : PL 66, figs. 1-19. 18S3. 
The figure is from the original specimen described.* It differs from S. con¬ 
tractus in its more robust, shorter and more rigid form, more obtuse post-inferior 
extremity, and more nearly vertical lower truncation of the posterior end. The 
supposed clavicle corresponds with the posterior limit of the anterior muscular 
impression as shown in fig. 9 of plate lxvi. 
Formation and locality. In the Yellow sandstones, at Burlington, la. 
* The specimens here described as /S'. contractus and /S'. arcuatus were identified by Mr. R. P. Whitfield 
as belonging to iSanguinolites rigidus, White and Whitfield, and thus referred in the Preliminary Notice 
of the Lamellibranchiata, 2 (above cited), and at the same time were thus arranged on the Plates for the 
Palieontology of New York, then being lithographed. A careful comparison of specimens with a cast of the 
original of /S', rigidus has shown the necessity of separating the Chemung species, and recognizing in one of 
the forms, the original of Ctjpricardia contracta, published in 1843. 
