124 
PALEONTOLOGY OF NEW-YORK. 
impressions are well defined, and between them there is a strong mesial 
ridge which is extended in a bidentate cardinal process. The lower half 
of the surface is strongly papillose. 
In general form, this species differs little from C. lineata (compare figures 3 
a-f and 4 a-g , Plate 20). It is less gibbous, and not flattened on the middle of 
the ventral valve; while the interior presents more strongly defined markings. 
In a collection of more than twenty specimens entirely separated from the lime¬ 
stone, which were sent me by the kindness of Dr. James Knapp, of Louisville, 
Kentucky, the general form and moderate convexity are preserved, and it is 
rarely that more than three spines are seen on one side of the centre; but this 
feature is subject to variation, and the spines are sometimes unequal on the two 
sides of the same specimen. 
All the differences indicated between this and the preceding species, I can 
readily believe may be produced in the same type by the different conditions 
of sea bottom, geographical distance, and other causes. 
Geological formation and localities . In the hydraulic beds of the Corniferous 
limestone, at the Falls of the Ohio, Louisville ( Kentucky), and Jeffersonville 
(Indiana). 
CSsonetes mucronata. 
PLATES XX & XXL 
Strophomena mucronata : Hall, Geol. Report 4th District New-York, p. 180, f. 3. 1843. 
Chonetes laticosta : Hall in Tenth Report on State Cabinet, p. 119. 1857. 
Shell small, semioval, moderately convex, nearly flat (often flattened in 
the shale and gibbous in the limestone) : cardinal line equalling or a 
little greater than the width of the shell below; the extremities 
sometimes salient. 
In the original specimens of this species from the Marcellus shale, the 
ventral valve is slightly convex or nearly flat, one-fourth to one-third 
wider than long : the hinge-extremities are rarely a little produced, 
but the spines lying in the direction of the hinge-line often give it the 
appearance of extreme extension. 
The dorsal valve is very moderately concave or nearly flat. 
The surface is marked by twenty to twenty-four or twenty-six nearly 
simple subangular striae, which are not so wide as the spaces between 
them. Sometimes one, two or three of these striae are bifurcated towards 
