CRYPTONELLA OF THE HAMILTON GROUP. 
395 
Geological formation and localities. This species occurs in the Hamilton group, 
at Bellona in Yates county; on the shore of Canandaigua lake ; at York, Moscow 
and Geneseo in Livingston county ; at Hamburgh on the shore of Lake Erie, and 
elsewhere in Western New-York. 
Cryptonella planirostra. 
PLATE LXI. 
Terebratula planirostra : Halt., Thirteenth Report on the State Cabinet, p. 89. 1860. 
« “ Id. Referred to Cryptonella in Fourteenth Report, p. 101. 1861. 
Cryptonella planirostra t Id. Sixteenth Report on the State Cabinet, p. 44. 1863. 
Shell subovate or elliptical; the front often truncate, giving a subpenta¬ 
gonal outline; the greatest width near the middle of the shell; the 
length and width about as six to seven or eight. The depth of the two 
valves, in well-formed specimens, is about equal to half the length. 
Ventral valve in old shells gibbous, the greatest convexity above the 
middle, often slightly flattened towards the beak, which is moderately 
incurved and truncate by a round foramen, limited below by conspi¬ 
cuous deltidial pieces, abruptly inflected along the umbonal slope, 
often leaving an angular ridge, and the space between it and the hinge- 
margin flat or concave; often slightly flattened below the middle, and 
regularly curving to the sides. 
Dorsal valve considerably shorter than the opposite, more convex or 
gibbous, the greatest convexity at or a little above the centre, curving 
to the sides and front where it is sometimes flattened : beak incur¬ 
ving beneath the deltidial plates of the opposite valve. 
Surface marked by fine rounded concentric striae, which in old shells 
are disposed in broader belts of imbricating lamellae. Shell-structure 
punctate. 
The crura reach below the middle of the length of the shell, 
approaching each other very closely, and abruptly recurved for a dis¬ 
tance about half their length : they are united near their bases by a 
transverse band. 
