PR0DUCTELLJ3 OF THE HAMILTON GROUP. 165 
Productella subalata. 
PLATE XXIII. 
Produdus subalatus : Tenth Report on the State Cabinet, p. 174. 1847. 
“ ■ “ Geological Report of Iowa, part .ii, pa. 500, pi. 3, f. 10. 
Shell semielliptical or semicircular, usually much wider than high; 
hinge-extremities equalling or less than the width of the shell. Ven¬ 
tral valve ventricose in the middle, gibbous on the umbo and towards 
the beak; extended, flattened and auriculate at the hinge-extremities : 
beak incurved over the hinge-line. There.is a distinct narrow area 
extending for more than half the length of the hinge-line. 
The surface is marked by fine concentric striae, with indications of radia¬ 
ting striae within the substance of the shell. The cardinal margins and 
the ears are marked by strong wrinkles which are often visible on the 
body of the shell. The spines are variable in number, often crowded 
together on the ears and adjacent portions of the shell, and irregularly 
scattered upon the middle and anterior part of the valve. 
This species is noticed in this place from its great similarity to the P. rarispina 
of the Chemung group of New-York. The specimen figured (PI. xxiii, f. 49) is a 
ventral valve above the prevailing size, with a greater extension of the hinge-line 
than usual. 
Geological formation and locality. In the calcareous shales of the Hamilton 
group at Rock island, Illinois. 
Product us ! -(sp.). 
PLATE XXIII. 
A single dorsal valve, of comparatively large size, occurs with P. spi- 
nulicosta, near Bellona in Yates county. When entire, it has had a length 
of about one inch and a quarter, with a width of an inch and a half. The 
interior of the shell is exposed, but the cardinal process is broken off, 
and there are no teeth-sockets visible. The surface is marked by slender 
pustuliform ridges, which become more elongate as they recede from the 
hinge-line, and on the middle and lower part of the shell are bifurcated, 
and show finer ridges between. 
This specimen cannot be clearly identified with any described form; but in 
the absence of other material, I hesitate to indicate it as a distinct species. 
Geological formation and locality. In the shales of the Hamilton group, near 
Bellona, Yates county. 
