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PALAEONTOLOGY OP 1 NEW-YORK. 
Hamburgh (Illinois) and in the town of Louisiana (Missouri), and in the calca¬ 
reous beds at the base of the Burlington limestone at Burlington (Iowa). 
In the Tully limestone there is a very extreme form, which, after careful com¬ 
parison, I can only regard as a variety of this species, having the front greatly 
produced. The beak is extremely incurved, and can only have been minutely if at 
all truncated. 
Froductella spinulicosta. 
PLATE XXIII. 
Productus spinulicosta : Hali, Tenth Report on the State Cabinet, p. 173. 1857. 
Shell broad, semielliptical or somewhat orbicular ; hinge-line generally 
a little less than the greatest width of the shell. 
Ventral valve varying in shells of different size, from moderately to 
extremely gibbous in the middle, with the beak strongly incurved. 
Dorsal valve moderately concave in its upper part, and becoming more 
concave or arcuate towards the front. 
Surface marked by fine strong concentric striae, which are sometimes 
crowded and wrinkled on the body of the shell. There are several rows 
of interrupted ridges or spine-bases, which in entire specimens support 
slender spines. The ears are strongly wrinkled, and support a row of 
four or five spines just below the hinge-line. 
The distinction between the species and the authentic specimens of P. shu- 
mardiana is not such as to entirely satisfy me of their specific difference. The 
specimens originally referred by me to this species are smaller than the prevailing 
size of P. shumardiana at Burlington, Iowa, and some of the younger individuals 
are somewhat broadly truncated at the apex. The spiniferous ridges are usually 
longer and more prominent than in the Burlington specimens. 
Geological formation and localities. In the calcareous bands of the Marcellus 
shale and in the shales of the Hamilton group, on the shores of Lake Erie, Cayuga 
and Seneca lakes and other places; 
Froductella truncata. 
PLATE XXIII. 
Productus truncatus : Hall ip Tenth Report on the State Cabinet, p. 171. 1857. 
Strophomena pustulosa : Hall, Geol. Report 4th District New-York, p. 189, f. 4. 1843. 
Not Productus pustulosus : Phillips. 
Shell small, concavo-convex : hinge-line equalling or less than the 
greatest width of the shell. 
